AN ABSTRACT OF THE THESIS OF
for the
John Byron Alexander
(Name)
Date thesis is presented
Title
!
M. S.
in
(Degree)
/1)
Geology
Major)
Q
STRATIGRAPHY AND TRUCTURE OF PART OF THE
FISH LAKE PLATEAU, SEVIER COUNTY, UTAH
Abstract approved
Major Pr ofessor)
Over 3, 000 feet of nonmarine Late Cretaceous sedimentary
rocks are exposed within the northern Fish Lake Plateau. The Cretaceous strata are overlain by over 2, 000 feet of Early Tertiary nonmarine sedimentary rocks and volcanics. Landslide deposits cover
over one-half of the area.
The Late Cretaceous Blackhawk Formation, the oldest forma-
tion exposed, was deposited in fluvial, swamp, coastal lagoon, and
possibly shallow marine environments during the eastward retreat of
the Mancos sea. This formation is overlain disconformably by the
Late Cretaceous Price River Formation which is composed largely of
quartz arenites derived from Paleozoic and Mesozoic sedimentary
rocks exposed to the west. The sediments were carried into the area
by streams and were deposited under piedmont and flood plain conditions.
The Late Cretaceous and Early Tertiary North Horn formation
conformably overlies the Price River Formation. The lower part is
composed largely of fluvial sandstones but, in the upper part, lacustrine mudstones and siltstones predominate. The latter were
deposited in the Uinta Lake which persisted until late middle Eocene.
In this lake the Early Tertiary Flagstaff, Colton and Green River Formations were deposited in succession. After an interval of erosion,
the Eocene Gray Gulch Formation was deposited and, later, lavas of
Oligocene age.
Two periods of folding are reflected by structures within the
area. The Early Laramide orogeny caused the disconformity between
the Blackhawk and Price River Formations, and a later period of
folding, between the late Eocene and Miocene, formed the Wasatch
and Gates Creek monoclines. Late Tertiary normal faulting has been
superimposed on the earlier structures.
There do not appear to be favorable structures for the accum-
ulation of oil and gas. However, stratigraphic conditions exist for
both the formation and accumulation of oil and gas. The Mancos
Shale, a known source rock for oil and gas farther to the east, is
present in the sub-surface. Sand pinchouts in Late Cretaceous strata
are believed to exist in the subsurface. Potential production in this
area will depend on the presence of these updip sand pinchouts.
STRATIGRAPHY AND STRUCTURE OF PART OF THE FISH
LAKE PLATEAU, SEVIER COUNTY, UTAH
by
John Byron Alexander
A THESIS
submitted to
OREGON STATE UNIVERSITY
in partial fulfillment of
the requirements for the
degree of
MASTER OF SCIENCE
June 1964
APPROVED:
In Charge of Major
"
/,V,
k 4,jlht-t"
Chairman of the Department of Geology
Dean
of Graduate School
Date thesis is presented
Typed by Trudie Vallier
'Q
/' /f65
ACKNOWLEDGMENTS
The writer wishes to thank the Union Oil Company of Califor-
nia for providing financial assistance during the fieldwork. Special
thanks are due to Mr. George H. Feister, of Union Oil Company of
California, who visited the writer in the field and offered valuable
suggestions and advice.
Appreciation is extended to Dr. Keith F. Oles, my major
R
professor, for his invaluable advice and careful editing of the manuscript. Acknowledgments are due the following members of Oregon
State University Department of Geology: Dr. W. D. Wilkinson, Chair-
man of the Department, who visited the writer in the field and critically read the manuscript; and Dr. Harold E. Enlows, who suggested
the thesis problem, accompanied the writer on a preliminary recon-
naissance of the thesis area, and also critically read the manuscript.
Special thanks are also extended to Mr. William Hill, Forest
Supervisor, Fish Lake National Forest, and to his assistants for
their help in obtaining maps and answering many questions concerning the region.
The writer would also like to thank the many inhabitants of
Salina, Utah and particularly Mr. and Mrs. Ivan Mills for their
hospitality and friendship.
TABLE OF CONTENTS
Page
INTRODUCTION .......................................
..........................
................
Previous Work .....................................
Location and Accessibility
Purposes and Methods of Investigation
..................................
Drainage ..........................................
Climate ...........................................
Vegetation .........................................
Relief.........
1
1
3
5
6
6
8
9
STRATIGRAPHY ....................................... .
...............................
...........................
.........................
.............................
........................
Regional Stratigraphy
Thesis Area Stratigraphy
Subsurface Stratigraphy
Surface Stratigraphy
Blackhawk Formation
Price River Formation .......................
North Horn Formation ...... ............... .
Flagstaff Formation
Colton Formation..
.... .................. .
....................... .
Green River Formation ......................
Gray Gulch Formation .......................
Tertiary Lavas ..............................
Unconsolidated Sediments ....................
STRUCTURAL GEOLOGY ...............................
.................................
..............................
Regional Structure
Thesis Area Structure
Folds ..........................................
Wasatch Monocline
Gates Creek Monocline .......................
74
74
76
76
.................................
76
78
78
Faults .........................................
Musinia Graben .............................
79
........................
81
GEOMORPHOLOGY ....................................
85
85
Terraces ..........................................
86
Landsliding ........................................
89
HISTORICAL GEOLOGY ................................
92
Other Folds
Water Hollow Graben
Stream Erosion ....................................
Pedimentation .....................................
82
87
TABLE OF CONTENTS (Cont.)
Page
ECONOMIC GEOLOGY .................................
Oil and Gas ........................................
Possible Reservoir Rocks ........................
Structural and Stratigraphic Traps ................
Oil and Gas Possibilities ........................
96
96
96
98
100
Coal ..............................................
100
BIBLIOGRAPHY .......................................
103
LIST OF FIGURES
Figure
1
2
Page
Gooseberry
Valley ...............................
7
Dip slopes formed on strata of the North Horn Formation ........................................
7
Vertical cliff formed by the Castlegate Member of
the Price River Formation
......................
22
4
Coal seam in the Blackhawk Formation ...........
22
5
Rose diagrams recording the results of measurements of foreset cross-laminations
24
3
6
7
8
9
10
11
12
13
...............
Outcrop of the Price River Formation in the Water
Hollow graben ..................................
28
Castlegate Member of the Price River Formation
rising out of the subsurface in Salina Canyon ......
28
Outcrop of the upper member of the Price River
Formation in Salina Canyon
....
.
30
Member of the Price River Formation ............
30
...............
Conglomerate and sandstone in the Castlegate
Cuesta in Gooseberry Valley formed on strata of
the North Horn Formation ..........
.......... .
Sandstone lense in the North Horn Formation along
Salina Creek ...................................
35
Outcrop of the Flagstaff Formation at the north end
of Gooseberry Valley ............................
41
Outcrop of Flagstaff limestone east of the Salina
Reservoir .....................................
14
15
35
45
The nearly horizontal Flagstaff Formation overlying steeply dipping strata of the Indianola Group
in Salina Canyon ................................
50
Gradational contact between the Green River and
the underlying Colton Formation in Gooseberry
...............................
Valley ........................................
53
LIST OF FIGURES (Cont.)
Figure
16
17
18
19
20
21
Page
Cross-bedded sandstones and conglomerates
within the Colton (?) Formation
..................
57
Outcrop of the Gray Gulch Formation north of Gates
Lake ..........................................
66
View south from near Salina Reservoir showing a
cliff formed by Tertiary lava flows
70
...............
Toe of the Wasatch monocline viewed from the center of Sevier Valley .............................
Drag fold in the Blackhawk Formation on the north
side of Salina Creek .............................
80
80
View of the western boundary fault of the Musinia
graben ........................
83
22
View north into Brown's Hole ....................
83
23
Pediment surface forming Flat Top Mountain between
88
Niotche and Yogo Creeks
24
........................
Landsliding in the southern part of the area, below
the lava covered plateau .........................
91
LIST OF PLATES
Plate
Page
........
2
subdivisions ...................................
4
1
Map of Utah showing location of thesis area
2
Index map of central Utah physiographic
3
Geologic map of part of the Northern Fish Lake
Plateau .......................................
102
LIST OF TABLES
Page
Table
1
Correlation chart ................................
2
Stratigraphic units exposed in the Northern Fish
Lake Plateau
3
....................................
Summary of oil and gas test holes in the thesis area..
12
18
97
STRATIGRAPHY AND STRUCTURE OF PART OF THE FISH
LAKE PLATEAU, SEVIER COUNTY, UTAH
INTRODUCTION
Location and Accessibility
The area investigated is located in the central part of Sevier
County, Utah, approximately 150 miles south of Salt Lake City
(Plate 1). It is rectangular in shape and is bounded by the meridians
1110311 and 111 °45' West Longitude and by the parallels 38°44' and
38°55' North Latitude. It includes parts of Townships 22, 23 and 24
North and Ranges 1, 2 and 3 South, Salt Lake Meridian.
This area lies in the northern part of the Fish Lake Plateau
and is within the Fish Lake National Forest. The Fish Lake Plateau
lies near the center of the High Plateaus province (Plate 2) and is
bounded on the north by the Wasatch Plateau, on the south by the
Awapa Plateau, on the west by the Sevier Valley, and on the east by
the Colorado Plateau province.
The northern edge of the area is crossed by Utah State
Highway 10, and a secondary road, maintained by the U. S. Forest
Service, passes in a north-south direction through the western part
of the area. From these roads a number of Forest Service and private access roads make most of the region readily accessible by
4-wheel drive vehicles. Using a vehicle of this type hiking distances
to any outcrop would rarely be over one-half mile. The roads at
the higher elevations are only open to traffic from July 1st to about
October 1 st because of heavy snow.
2
IDAHO
WYOMING
z
Provo
UTAH
Price
Delta
Thesis
Green River
Are a
Cedar City
40
80120
Scale of Miles
ARIZONA
PLATE 1. Map of Utah showing location of thesis area.
3
Purposes and Methods of Investigation
The primary purposes of the thesis problem were: (1) to map
the surface geology of the area; (2) to delineate the major structures
of the area; (3) to study those sedimentary facies changes which might
be of potential petroleum significance.
Field work began on June 28, 1964 and was completed Septem-
ber 15, 1964. The surface geology was plotted on high altitude
(1:60, 000) aerial photographs obtained from the U. S. Geological
Survey and was transferred to U. S. Forest Service planimetric maps..
Modern, large scale topographic maps are not as yet available for
this area.
Formation thicknesses were computed from outcrop widths
and from electric logs. No stratigraphic sections were measured as
data was available from well logs and from published information col-
lected in adjacent areas.. Attitudes of foreset cross-laminations
were measured and rosette diagrams (Figure 5) were prepared in an
attempt to determine the direction of source areas. Twenty-five thin
sections and fifteen grain mounts were prepared from selected samples and studied microscopically.
Most lithologic descriptions were done in the field with the aid
of a lOX hand lens. The classification of sandstones followed in this
thesis is that described by Gilbert (30, p. 289-297). In describing
argillaceous sedimentary rocks, the classification of Ingram (11, p.
869-878) was used. The calcareous sedimentary rocks were classi-
fied according to the system proposed by Folk (6, p. 1-38).
4
1120
Utah
Lake
BASIN
Price
Sevier
Lake
Thesis
Are
Fish
'
Lake
'Iateat
Tuehor
Lk JV 1-Table
Cliffs Plgtsau
,sue 10
l IQ
Plate
0
112°
5________op
11
2. Index map of central Utah physiogrophic subdivisions (modified after Woolley, 1947,
P1.4). Heavy line indicates the High Plateau province.
5
Previous Work
The northern part of the Fish Lake Plateau was studied by C.
E. Dutton (5). This study was of a reconnaissance nature since Dutton
was primarily interested in the thick succession of igneous rocks and
pyroclastics of the southern High Plateaus. In his report Dutton in-
cluded a stratigraphic discussion and stratigraphic sections by E. E.
Howell based on traverses of the area during 1873 and 1874. The thesis area was not treated in detail.
A reconnaissance ground-water report by Richardson (19) and
a surface-water resources report by Woolley (31) included the area
but did not give information concerning the bedrock.
The Wasatch Plateau and adjacent areas have been the subject
of an extended study by E. M. Spieker (21, 22, 23, 24, 25, 26). The
only work done by Spieker (25) south of the Wasatch Plateau concerned
the coal reserves of the Salina Canyon district. The geology of the
Wasatch Plateau was summarized by Spieker (23) in his discussion of
the region as a transition zone between the Colorado Plateau and the
Great Basin.
The northern part of the Fish Lake Plateau was mapped by
Donald P. McGookey as partial fulfillment of the requirement for a
Ph. D. degree at Ohio State University. An article by McGookey (16)
concerning the Early Tertiary strata of areas west of the Gates Creek
Monocline, was published in the Bulletin of the American Association
of Petroleum Geologists.
6
Relief
Elevations in the area range from a minimum of 5, 800 feet in
Gooseberry Valley (Figure 1) to a maximum of 10, 600 feet in the ex-
treme southern part of the area on the lava-covered Fish Lake Plateau
(Plate 3). The maximum relief is approximately 4,800 feet.
Generally the region slopes to the north and northwest from the
lava-covered highlands of the Fish Lake Plateau. In the northwest
part of the area the distinguishing features are prominent dip slopes,
dipping westward into Gooseberry Valley (Figure 2). In the southern
part of the area, north of the lava-covered plateau, rounded hills and
slopes, formed by extensive landsliding, are common features. The
northeastern sector is characterized by nearly flat upland areas interrupted by steep walled canyons. The canyons, with a maximum relief
of 1, 000 feet, have been produced by Salina Creek and its tributaries.
Drainage
The mapped area is drained principally by north-flowing
perennial and intermittent streams which are tributary to Salina
Creek. The latter, which flows to the west, is located in the extreme
northern part of the area (Plate 3). Salina Creek is tributary to the
Sevier River which terminates in Sevier Lake, south of Delta, Utah.
Localities adjacent to the mapped area on the east and south.are
drained by south-flowing tributaries of the Fremont River. This
stream flows to the east and is a tributary of the Colorado River.
The north-flowing streams which drain the region are generally subsequent to the north-south structures but some streams,
7
FIGURE 1. View south up Gooseberry Valley.
The valley is formed on strata of the North
Horn, Flagstaff and Colton Formations. Distant dip slopes are formed on strata of the
North Horn Formation.
FIGURE 2. Dip slopes formed on strata
of the North Horn Formation dip westward into Gooseberry Valley. Sandstones
of the Price River Formation form the
cliffs in the foreground. West of Gooseberry Valley are cuestas formed on
limestones of the Green River Formation.
8
such as Niotche Creek and Salina Creek (Plate 3), flow across northsouth trending faults with-out any change in direction and appear to be
antecedent to the structures.
Climate
The nearest U. S. Weather Bureau station is at Richfield,
Utah, 20 miles to the southwest. A U. S. Forest Service weather
station is located within the mapped area in sec. 16, T. 23 S. , R.
2. E.
The mean annual temperature within the area is about 400 F.
January is the coldest month with temperatures often falling below
-150 F.. July is normally the warmest month, with temperatures
reaching 800 F. at the higher elevations, and occasionally exceeding
1000 F. at the' lower elevations.
The area receives approximately 10 to 15 inches of precipitation per year. The maximum amount of rain falls during the summer
months when thunderstorms occur almost daily. The thundershowers,
which occur on the average of 50 days a year, cause flash-floods
which are an important agent of erosion. The Forest Service is presently conducting experiments within the area in an attempt to minimize
such erosion.
Most of the winter precipitation is in the form of snow which
accumulates to depths in excess of 40 inches. The higher elevations
are usually covered by snow from November through May.
9
Vegetation
Most of the area is heavily vegetated and in some places the
vegetative cover is a hindrance to geological field work. There are
well developed floral zones controlled by elevation. The lower areas
and highland meadows are covered by grasses and low shrubs. On
the steeper and drier slopes scrub oak (Quercus gambelii) predominates. Aspen (Populus tremuloides) grow in profusion along the
creek bottoms and in landslide areas. Pines (Pinus edulus), junipers
(Juniperus utahensis), and firs (Pseudotsuga menziesii) are found at
the higher elevations in the southern part of the area.
Some farming is practiced in Gooseberry Valley, where hay
is the major crop. Most of the area is used for summer range.
Large bands of sheep graze at the higher elevations and cattle graze
in the lower meadows and canyons. The central part of the thesis
area is within a U. S. Forest Service Experimental Area in which
observations are made on plant populations, rates of growth and
stream run-off.
Outside of the landslide areas (Plate 3) the outcrops are generally good, except where they are obscured by thick stands of aspen
and scrub oak.
10
STRATIGRAPHY
The mapped area is located in the High Plateaus of Utah
(Plate 2) which are a transition zone, both in land forms and geology,
from the Great Basin on the west to the Colorado Plateau on the east.
The rocks of the High Plateaus and adjacent regions range in age from
Precambrian to Quaternary.
Regional Stratigraphy
The discussion of regional stratigraphy will be restricted to
an area bounded on the north by the southern end of the Wasatch
Mountains, on the south by the Markagut and Paunsaugunt Plateaus,
on the west by the Pavant and Canyon Ranges, and on the east by the
San Rafael Swell.
A thick section of Precambrian argillites and quart zites crops
out east of Salt Lake City in the southern Wasatch Mountains. Other
Precambrian rocks are exposed in the Canyon Range, about 35 miles
northwest of the Fish Lake Plateau, where 8, 000 feet of quartzites
and limestones are thrust over younger strata.
Thick sections of Paleozoic rocks, ranging in age from Cambrian to Devonian, are found in the Pavant and Canyon Ranges to the
west and northwest of the thesis area. Quartzite, shale, limestone
and dolomite are the dominant rock types, and the sections range in
thickness from over 5, 000 feet in the Pavant Range to over 10, 000
feet in the Canyon Range.
The oldest Mesozoic rocks found west of the High Plateaus
11
are cross-bedded sandstones of the Jurassic Navajo Formation
(Table 1). These crop out in the Pavant Range and at the base of the
southern Wasatch Mountains near Thistle, Utah. Overlying the
Navajo Formation in the Sevier and San Pete Valleys is the Jurassic
Arapien Shale which consists of about 10, 000 feet of shale, siltstone,
sandstone, limestone, and local commercial deposits of rock salt
and gypsum. Overlying the Arapien Shale at many localities is a 300
to 400 foot section of varicolored sandstones and conglomerates that
Spieker (23, p. 18) has tentatively correlated with the Morrison Formation of the San Rafael Swell.
The oldest Cretaceous rocks exposed on the western border
of the High Plateaus are units of the Indianola Group of Colorado age.
West of the Wasatch Plateau, Spieker (23, p. 21) reports that the
Indianola Group ranges in thickness from 8, 000 to 15, 000 feet and is
composed of conglomerate and sandstone, with minor shale and limestone. The Indianola Group cannot be traced on outcrop any farther
east than the west flank of the Wasatch Plateau, where the unit is
about 6, 300 feet thick, but it is probable that the Indianola becomes
finer grained to the east and grades into the middle and lower Mancos
Shale (12).
East of the High Plateaus spectacular exposures of Triassic,
Jurassic and Cretaceous rocks crop out on the San Rafael Swell
(27, p. 23-35). The Triassic section attains thicknesses of about
1, 800 feet and is composed of a variety of continental sediments.
About 4, 000 feet of Jurassic rocks are exposed on the San Rafael
Swell and they are composed of a number of rock types which are of
12
T
Sevier-Sanpete
Valleys-Wasatch
Plateau (West)
San Rafael Swell
Plateau
Thesis
re
Green River
Desert-San
Rafael Swell
(East)
Tertiary Lavas
OLIGOCENE
Gray Gulch Fm.
EOCENE
P4
PALEOCENE
Crazy Hollow Fm.
-----------------
Green River Fm.
Colton Fm.
Green River Fm.
Flagstaff Fm.
Flagstaff Fm.
Flagstaff Fm.
North Horn Fm.
North Horn Fm.
North Horn Fm.
Price River Fm.
Price River Fm.
0 Price River Fm.
Colton Fm.
Blackhawk Fm.
Blackhawk Fm.
Star Point Ss.
Star Point Ss.
Emery Ss.
M asuk Sh.
Emery Ss.
Z
O
UPPER
cn
Six Mile
Canon Fm.
w O
FQ
a
O
U U
0
d
10
En Blue Gate Sh.
Blue Gate Sh.
ug
Funk Valley Fm Ferron Ss.
Allen Valley Fm
Ferron Ss.
o
U
Tununk Sh.
Tununk Sh.
Cd
Dakota
0
Ferron Ss.
Dakota Ss.
Ss.
,a
4
Sanpete Fm.
LOWER
Lower Cretaceous
and Morrison
(undivided)
UPPER
(n
Twist Gulch
Mbr.
F
Twelve Mile
U
< MIDDLE
?
Morrison
Canyon Mbr.
?
I
!I
I
1=
Cedar Mt. Fm.
Morrison Fm.
Morrison Fm.
Summerville Fm.
Curtis Fm.
Summerville Fm.
Entrada Ss.
Entrada Ss.
Carmel Fm.
Carmel Fm.
Curtis Fm.
1i
Navajo Ss.
LOWER
Cedar Mt. Fm.
x
? r_ez
Navajo Ss.
Navajo Ss.
Kayenta Fm.
Kayenta Fm.
I
I
Compiled by J. Alexander from various sources.
13
both marine and nonmarine origin. Only three Jurassic Formations
can be correlated with units west of the Wasatch Plateau: the Navajo
Sandstone, the Carmel Formation, which is correlative to the
Arapien Shale, and the Morrison Formation. The Early Cretaceous
rocks, represented by the Cedar Mountain Formation and the Dakota
Sandstone, are chiefly nonmarine and surround the San Rafael Swell
in a nearly continuous band. The Late Cretaceous Emery and Ferron
Sandstones and the Mancos Shale crop out in Castle Valley and on the
long slopes at the base of the east front of the Wasatch Plateau. The
Mesaverde Group overlies and intertongues extensively with the
Mancos Shale and these mixed marine and nonmarine beds form the
Book Cliffs, the imposing series of cliffs rising above the lowlands
around the San Rafael Swell.
Outcrops of Late Cretaceous sedimentary rocks, including the
Blackhawk, Price River and North Horn formations, are widespread
in the northern part of the Fish Lake Plateau and throughout the
Wasatch Plateau. These units attain an aggregate thickness of over
5, 000 feet in some areas and are composed of piedmont, flood plain,
lagoonal and marine sedimentary rocks.
A thick sequence of Early and Middle Tertiary sedimentary
and volcanic rocks, including the Flagstaff, Colton, Green River,
Crazy Hollow and Gray Gulch Formations, overlies the older rocks
of the region. The Tertiary sedimentary rocks are widespread in
the Wasatch and Fish Lake Plateaus and on the east flanks of the
Pavant and Canyon Ranges. They are composed predominantly of
varicolored and calcareous lacustrine deposits which attain
14
thicknesses of over 5, 000 feet. A thick series of andesitic lava flows
covers over 3, 000 square miles of the High Plateaus south of the
Wasatch Plateau. These flows are of Oligocene age and unconform-
ably overlie older eroded sedimentary rocks. Other lavas and associated volcanic rocks are found on the western side of the Gunnison
Plateau and in the eastern part of the Cedar Hills near Thistle, Utah.
Quaternary glacial moraine, landslide, and alluvial deposits
are found within the region. The glacial deposits and landslides are
generally restricted to the highlands of the High Plateaus. Alluvial
deposits blanket the floors of the Sevier and San Pete Valleys, but
within the High Plateaus alluvium is absent except in a few of the
larger valleys.
Thesis Area Stratigraphy
Rocks ranging in age from Late Cretaceous to Oligocene are
exposed in the northern part of the Fish Lake Plateau. Some knowledge of subsurface stratigraphy is known from two oil and gas test
holes that have been drilled within the mapped area. In the following
sections a summary of the known subsurface stratigraphy will be
presented, followed by detailed descriptions of the exposed units.
Subsurface Stratigraphy
Over 5, 000 feet of Late Jurassic and Early Cretaceous sedi-
mentary rocks not exposed in the thesis area, have been penetrated
by two oil and gas test holes, the El Paso Natural Gas Company
Unit No. 1 drilled in sec. 15, T. 22 S., R. 2 E., and the Pan
15
American Petroleum Corporation Porcupine Ridge Unit No. 1 drilled
in sec. 30, T. 22 S., R. 3 E. (Plate 3).
The oldest formation penetrated was the Morrison Formation
(Table 1) of Late Jurassic and Early Cretaceous Age which was tested
by the El Paso Natural Gas Company. Interpretation of the well log
of this hole indicates that the top of the Morrison Formation is composed predominantly of sandstone. This is to be expected as six miles
west of the test site nearly vertical beds of the Morrison Formation
crop out and are composed of sandstones and conglomerates.
It is noteworthy that other Early Cretaceous strata are missing in the thesis area but are represented 20 miles to the east on the
west flank of the San Rafael Swell.
The Pan American well penetrated the Tununk Shale Member
of the lower Mancos Shale of Late Cretaceous age, but the El Paso Natural Gas Company test hole, located two and one half miles to the northwest,
did not. Where the Tununk Member would be expected the test hole
penetrated the Sanpete Formation of the Late Cretaceous Indianola
Group. This fact is strong evidence that the Indianola Group becomes
progressively finer-grained to the east and merges with the lower
part of the Mancos Shale.
Both test holes penetrated the Late Cretaceous Ferron Sandstone and the overlying Blue Gate Member of the Mancos Shale. The
Ferron is composed of fine- to medium-grained sandstone interbedded
with thin siltstone and shale units. A few coal beds are present and
in the Pan American hole positive oil staining was reported from the
upper 100 feet of the formation. The formation appears to have a
16
constant thickness of about 700 feet between the two wells. The Blue
Gate Member represents the middle part of the Mancos Shale and is
composed of calcareous shales and siltstones with a few interbedded
sandstones. The unit thins from 1, 590 to 690 feet, from east to west,
between the two test holes. This thinning represents the regression,
to the east, of the Mancos sea during the Late Cretaceous.
The Emery Sandstone of Late Cretaceous age was recorded
in the El Paso Natural Gas hole but not in the Pan American hole.
From a study of the well logs it appears that in the Pan American
well the Emery and Ferron formations have not been differentiated.
The two formations were probably grouped together because the
Masuk Member of the Mancos Shale, which separates them in eastern
Utah, is not present in the thesis area. In the El Paso Natural Gas
Company hole the Emery Sandstone is the first stratigraphic unit recorded and has a thickness of 480 feet. In the Pan American test hole
the two formations are represented by over 2, 000 feet of fine- to
medium-grained calcareous sandstone interbedded with a few thin
siltstone and shale units.
The Star Point Sandstone is considered to be the basal unit of
the Mesaverde Group and the strata represent deposition in a transition zone between the marine Mancos Shale and the predominantly
continental strata of the Mesaverde Group. The upper surface of the
Star Point Sandstone represents the passage from littoral marine
and brackish water sandstone to the continental beds of the Blackhawk
Formation. Cretaceous formations younger than the lower part of
the Blackhawk formation are exposed within the mapped area and
17
will be discussed in the following section.
Surface Stratigraphy
Blackhawk Formation
The Blackhawk Formation of Late Cretaceous age, named by
Spieker and Reeside (26) for prominent exposures of coal-bearing
sandstones and shales near the Blackhawk Mine on the east front of
the Wasatch Plateau, is the oldest formation exposed in the mapped
area. The formation consists of coal-bearing continental strata lying
between the Star Point Sandstone, which is the basal unit of the Mesa-
verde Group, and the overlying Price River Formation. The base of
the formation is not exposed within the thesis area but eight miles to the
east the Blackhawk Formation conformably overlies the.Star Point
Sandstone (26). The upper contact is drawn at the base of the cliff-
forming Castlegate Member of the Price River Formation. In most
of the area this contact is obscured by rock debris but where the
contact can be observed it represents a disconformity. The Price
River Formation was deposited on an erosional surface of very low
relief cut into the uppermost Blackhawk rocks. This disconformity
when traced to the west changes to an angular unconformity in a fold-
ed belt three miles east of Salina, Utah. The angular unconformity
represents the main Laramide orogeny in central Utah, which occurred between Middle and Upper Montana time (23, p. 79).
Distribution and Topographic Expression. The Blackhawk
Formation is widely exposed in the Wasatch Plateau and in the Book
Cliffs of eastern Utah where it thins and intertongues with the upper
18
TABLE 2. Stratigraphic units exposed in the northern Fish Lake
Plateau.
Thickness
Age
Map Unit
Recent
Alluvium and
Recent
Lan d s lid e d epos i ts
Pliocene (?)
Pediment gravels
terrace deposits
Lithology
(feet)
?
Unconsolidated and poorly
sorted silt, sand, gravel
and boulders.
Unconsolidated clay, sand,
and gravel, depending on
bedrock.
0-30
Boulders of lava and sedimentary rock in a matrix
of pebbles and sand.
Oligocene
Tertiary lavas
2001000
Gray to chocolate colored
lava flows of andesitic
composition.
(Unconformity)
Oligocene
Bullion Canyon
volcanics, clastics
2, 500
Gray igneous rock con-
glomerate, coarse tuffa-
ceous sandstone and mud
mudflows.
(Disconformity)
Eocene
Gray Gulch
Formation
1, 250
Gray tuffaceous sandstone
containing glass and light
gray to white shale, limestone and tuffaceous sandstone.
Eocene
Crazy Hollow
Formation
1, 000
Red shale and siltstone,
gray salt-and-pepper
sandstone.
300-
Upper part: light gray
massive and thin-bedded
(Disconformity)
Eocene
Green River
Formation
1, 150
limestone. Lower part:
green mudstone and siltstone.
Eocene
Colton Formation
550
Red and orange mudstone
and siltstone, mottled
with gray.
19
TABLE 2. Continued.
Age
Paleocene
Map Unit
Thickness
(feet)
Flagstaff
Formation
90-
Paleocene
Late
Cretaceous
North Horn
Formation
1, 200
Late
Cretaceous
Price River
Formation
1, 100
300+
Lithology
Red silt stone and limestone in northwestern
part; gray and white limestone and shale in central
and southern part of area.
Red, orange, and gray
shale, gray fluviatile
sandstone s .
Upper member: gray medium to coarse sandstone;
Castlegate Member: gray
to white cliff-forming
sandstone.
(Di s c onfo rmity)
Late
Cretaceous
Blackhawk
Formation
(Base not exposed)
450+
Gray to brown fluviatile
sandstones; gray shale
and thin coal seams.
20
part of the Mancos Shale (32). Within the mapped area the most ex-
tensive exposures of the formation are in Salina Canyon and in the
tributary canyons to the south (Plate 3). The topographic expression
of the formation is of a bench and bluff nature with step-like slopes of
mudstones and shales between 10 to 20 foot cliffs of sandstone
(Figure 3).
Lithology and Thickness. The Blackhawk Formation consists
of a monotonous sequence of sandstones, mudstones, shales and thin
coal beds. The sandstones are 2 to 20 feet in thickness and are light
gray in color when fresh and darker gray to red brown in color when
weathered. They are generally cross-bedded and show cut and fill
structures which indicate a fluviatile origin. Thirty-four measure-
ments of foreset cross-laminations suggest a source direction from
the west (Figure 5). The sandstone units are composed dominantly
of sub-rounded to rounded, fine- to medium-grained quartz and chert,
Some units are composed of clean quartz sand cemented with calcium
carbonate; others contain abundant lithic fragments and ferruginous
material which, upon weathering, stains the beds a dark brown to
red color. Petrographic analysis of one representative sample indicates a composition comparable to that of a quartz arenite. Hand
specimen analysis of the sandstones containing abundant lithic frag-
ments and iron oxide cement indicates that they are quartz wackes.
Dark gray fissile shales and gray even-bedded mudstones are
interbedded with the sandstones. The mudstones and shales are us-
ually sharply defined from one another and from the sandstones, in-
dicating rapid changes in the characteristics of the materials supplied
21
and in the environments of deposition. The shale units are generally
less than five feet thick while the mudstones range in thickness from
a few inches to 20 feet. The coal beds are generally less than two
feet thick and grade downward into carbonaceous shale and are over-
lain by shale or sandstone (Figure 4). The contacts between the coal
and the overlying shales are both gradational and sharp, but where
sandstone overlies the coal beds the contacts are generally sharply
defined. Some load structures were observed where the coal has
been forced up into the overlying sandstones.
The sharp contacts
between the coals and sandstones indicate rapid changes in the envi-
ronment of deposition, and the load structures indicate that the coal
beds were covered by the coarser material prior to their consolidation.
In the Wasatch Plateau the Blackhawk Formation ranges in
thickness from 700 to 1, 500 feet and thins to the east (26, p. 444).
Within the mapped area the thickness of the formation, as interpreted
from well logs, is about 500 feet.
Age. The coal beds within the Blackhawk Formation consist
of bundles of coniferous filaments with a few conifer pollen grains
and some fern spores (26). Plants collected by Spieker (21, p.
indicate a Montana age for the formation.
136)
In the mapped area many
plant fossils occur within the formation but they are poorly preserved
and not identifiable.
Source Rocks and Depositional Environments. The predominance of quartz grains, their high degree of rounding and fine to
medium size, indicate that the sand grains have either had a long
t;1.,4
r
1.
Y -
j
`
(:
'.
j
t:,
aft r;;, ,
.i
+
l
mar! fir[
i
`,
ICI
k
.r.-w
FIGURE 3. A vertical cliff formed by the Castlegate Member of the Price River Formation over-
,yam
lies steep ledge-broken slopes formed on sandstones and mudstones of the Blackhawk Formation. Salina Canyon.
FIGURE 4. A two foot coal seam interbedded
with sandstones of the Blackhawk Formation.
Salina Canyon.
23
history of transportation and reworking or have been recycled.
Thirty measurements of foreset cross-laminations in fluviatile sandstone units from four localities suggest that the sandstones were de-
rived from source areas to the west (Figure 5). The clastic fraction
of the formation was probably derived from pre-existing Triassic and
Jurassic sandstones which were uplifted and subjected to erosion during the formation of the Sevier Arch. The Sevier Arch, as described
by Harris (9), was located in southern Nevada and Central Utah and
was uplifted in the Late Jurassic or Early Cretaceous, providing
clastic material to central and eastern Utah until the Early Tertiary.
In the early stages of erosion the Sevier Arch furnished coarse material which formed the sandstones and conglomerates of the Indianola
Group of Colorado age. This group attains a thickness of nearly 15,
000 feet west of the southern Wasatch Mountains (23, p. 21). However, by Middle Montana time the highlands of the Sevier Arch had
been worn down considerably and were supplying only fine- to medium-
grained material to the sedimentary environments in which the Blackhawk Formation was being deposited.
To the east, in the Book Cliffs area, the Blackhawk Formation, as described by Young (32), intertongues extensively with the
marine Mancos Shale and is characterized by littoral marine sandstone tongues which, projecting eastward into the Mancos, lose their
identity by grading into shale. Above each littoral sandstone tongue,
Young described lagoonal deposits of sandstone, shale and coal that
were developed behind barrier bars. Young interpreted the intertonguing sandstones and the lagoonal deposits as the result of
24
N
N
11)
14)
(131
(8)
(7)
(7)
(5)
(14)
(6)
(4)
W
W
E
(2)
E
(5)
(12)
(1
(6
(6)
(5)
2)
12)
(7)
S
A.
North Horn Formation
B.
(18)
Price River Formation
W
S
C.
Black Hawk Formation
FIGURE 5. Rose diagrams recording the results
of measurements of foreset cross-laminations in
the Blackhawk, Price River, and North Horn For-
mations.
25
deposition in a shallow basin in which there were long periods of
stability separated by sharp pulses of basin subsidence.
West of the Book Cliffs, within the mapped area, none of the
strata were definitely proved to be of marine origin but it is possible
that some of the shales and mudstones represent marine deposition.
However, the sandstones, which are the dominant single lithologic
type in the mapped area, indicate a fluviatile environment of deposition. Cross-bedding and cut and fill structures support this conclusion.
The intercalated coal beds and carbonaceous shales containing
leaf fossils suggest a swamp or coastal lagoon environment. These
similarities and dissimilarities to the Blackhawk Formation of the
Book Cliffs, as described by Young, indicate that the various units of
the formation were deposited, from west to east, in piedmont fluvia-
tile, swamp, coastal lagoon, and possibly shallow marine environments and that during Blackhawk time the Mancos sea retreated
eastward as sediments spread into the marine basin. Periods of
accelerated basin subsidence caused successive reinvasions of the
sea resulting in the intertonguing of marine, transitional and continental sediments.
Price River Formation
The Price River Formation was named by Spieker and
Reeside (26) for a series of noncoal-bearing sandstone, grit and
conglomerate beds lying above the Blackhawk Formation. It includes
the upper part of the Mesaverde Group and derives its name from
exposures in Price Canyon, west of Castlegate, Utah. In typical
26
development the formation consists of a basal sandstone, the Castlegate Member, which forms extensive cliffs, and an unnamed upper
member, composed of sandstones and mudstones, which forms a
bench and bluff topography rather than an unbroken cliff.
The Price River Formation disconformably overlies the
Blackhawk Formation (Figure 2). The beds of the respective forma-
tions are parallel and the precise location of the contact is difficult
to locate. In practice the contact is drawn where there is an abrupt
change from a section of alternating sandstones and shales with coal
beds, to one composed predominantly of sandstone.
The sandstones of the upper member of the Price River Formation grade into and intertongue with the overlying varicolored mud-
stones and sandstones of the Late Cretaceous and Early Tertiary
North Horn Formation. The boundary between the formations is
purely lithologic in nature and is placed at the base of the varicolored
beds of the North Horn.
Distribution and Topographic Expression. The Price River
Formation crops out extensively in Central Utah: in the Gunnison,
Wasatch and Fish Lake Plateaus, westward in the Pavant Mountains,
and eastward in the Book Cliffs. Within the mapped area the forma-
tion is exposed in Salina Canyon and in tributary canyons to the south
where it forms steep cliffs above the underlying Blackhawk Formation. The upper member of the formation rises out of the subsurface
in sec. 7, T. 22 S., R. 2 E., and the underlying Castlegate Member
is first exposed in sec. 8, T. 22 S. , R. 2 E. (Figure 7). The
Castlegate Member at the base of the formation forms an unbroken
vertical cliff 150 to 200 feet high (Figure 6). The upper unnamed
member is a cliff-former in part, but generally forms steep slopes
interrupted by ledges of resistant sandstone.
Lithology and Thickness. Within Salina Canyon the Castle-gate
Member consists of 200 feet of fine- to coarse-grained sandstone, a
few thin conglomerates, and thin mudstone units. The sandstones,
which are locally conglomeratic, are light gray to white in color
when fresh and weather to yellow gray and buff. They are cross-
bedded and display cut and fill structures indicating their fluviatile
origin. The sandstones are composed predominantly of sub-angular
to sub-rounded, fine- to coarse-grained quartz and chert grains
weakly cemented by carbonate. In two samples which were sectioned
iron oxide forms a large percentage of the cementing material.
These sandstones are classified as quartz arenites.
Conglomerate units within the Castlegate Member are limited
in occurrence whereas in areas to the northwest, near Manti, Utah,
they are the dominant rock type (23, p. 23-24). The conglomerates
in the mapped area are light gray to buff in color when fresh and
dark gray to yellow brown when weathered. They occur in units
ranging from 1 to 15 feet in thickness. The clasts are predominantly
less than two centimeters in diameter and are composed of well-
rounded white and black quartzite and chert pebbles (Figure 8) and,
locally, angular- to sub-angular white limestone pebbles. The limestone clasts probably indicate that the units were derived from more
than one source. The matrix is composed of sub-angular to sub-
rounded, medium- to coarse-grained quartz and chert grains which
n
(
L
-
-
-
FIGURE 6. A near vertical cliff formed by resistant sandstones of the Castlegate Member of the
Price River Formation. The outcrop is located
in Salina Canyon within the Water Hollow graben.
The steep slopes in the left foreground are formed on strata of the Blackhawk Formation.
FIGURE 7. The Castlegate Member rising from
the subsurface in Salina Canyon. The steep
slopes above the Castlegate cliff are formed by
the upper member of the Price River Formation.
29
are weakly cemented by carbonate and iron oxide.
A few gray mudstone beds, generally less than one foot thick,
are interbedded with the sandstones. The sandstones grade into the
overlying mudstones but the contacts between the sandstones and the
underlying mudstones are usually sharp.
The upper unnamed member, which is about 800 feet thick,
is lithologically different from the Castlegate Member, the major
differences being that the Castlegate Member tends to be more con-
glomeratic, and the upper member has thin, well-bedded, gray, red
and brown shale and mudstone units interbedded with the sandstones.
The upper member is characterized by a persistent white, fine- to
medium-grained, cross-bedded, cliff-forming sandstone unit
(Figure 9). This unit is 20 feet thick and is located about 150 feet
above the top of the Castlegate cliff. This is a good marker unit and
is recognizable throughout the area. Ferruginous concretions, gen-
erally less than one centimeter in diameter, are found within both
members of the formation but are more common in the upper mem-
ber.
Within the mapped area the Price River Formation has a
uniform thickness of about 1, 000 feet. The unit apparently thickens
to the northwest as Spieker (23, p. 24) reports thicknesses in excess
of 2, 000 feet on the west front of the Wasatch Plateau.
Age. The age of the Price River Formation has been determined from mollusks, collected by Spieker (26) from the Wasatch
Plateau, which are characteristic of the Late Montana stage of the
Late Cretaceous. In eastern Utah the Castlegate Sandstone,
itM%t -ate
41.
d
FIGURE 8. Outcrops of the Price River For-
mation. The light-colored cliff-forming sandstone in the center of the photograph is a per-
sistent marker unit near the base of the upper
member. Salina Canyon.
`A1
FIGURE 9. An outcrop of the Castlegate Member of the Price River Formation composed of
alternating pebble conglomerates and coarsegrained sandstones. Salina Canyon.
31
occurring as a littoral tongue in the Mancos Shale, has also been
dated as Late Montana by marine fossils within the enclosing Mancos
shales. Other than some wood fragments and a few thin coal stringers
with plant fragments, no fossils were found within the mapped area.
Source Rocks and Depositional Environment. The fact that the
sandstones of the Price River Formation are generally clean and composed predominantly of quartz grains suggests that the sand grains
have had a long history of transportation and reworking or that they
have been recycled. The conglomerate units, composed of clasts of
quartzite and chert are also indicative of a mature sediment. The
lack of rounding of the sand grains indicates that the grains have not
undergone extensive transportation. They were probably derived from
pre-existing sandstone units. North of the mapped area, in the vicin-
ity of Manti, Utah, the Price River Formation is predominantly conglomeratic and is lithologically indistinguishable from the underlying
Indianola conglomerates of Colorado age. There appears to be little
doubt that the Price River conglomerates and sandstone were derived
from these older units during the early erosion of highlands to the
west. These highlands, west of the present Sevier and Sanpete
Valleys, were produced by thrust faulting which marked the beginning
of the Laramide orogeny (9). The lack of thick conglomerate beds
and the predominance of fine- to medium-grained sandstones within
the mapped area indicate a marked facies change from the piedmont
environment which existed to the northwest to an environment of
flood plain and channel deposition.
To the east in the Book Cliffs, the Price River Formation,
32
as described by Young (32), thins eastward and intertongues with the
Mancos Shale. Young states that from west to east the formation dis-
plays characteristics of flood plain, lagoonal, and littoral marine
deposition, and that west of Grand Junction, Colorado the formation
is represented by littoral marine sandstone tongues which pass transitionally into the Mancos Shale. The facies changes from west to east
indicate that within the mapped area the units of the Price River Formation were deposited as flood plain and channel deposits, and that
the area represents a transition zone between the piedmont environment to the west and the lagoonal and littoral marine environments to
the east.
One hundred and ten measurements of foreset cross-laminations from 14 localities do not indicate a specific source direction for
the sandstones but suggest a source from the west (Figure 5). The
lack of consistency in the foreset directions is believed to be a result
of the fluviatile and channel conditions under which the formation was
deposited.
North Horn Formation
The North Horn Formation was first defined by Spieker and
Reeside (26), as the lower member of the Wasatch Formation. Later,
the discovery of vertebrate fossils indicated that the lower part of the
formation was Late Cretaceous rather than Early Tertiary in age.
Spieker (21, p. 120) redefined the unit as the North Horn Formation
and named as the type locality a section exposed at North Horn Moun-
tain on the east side of the Wasatch Plateau. The formation typically
33
consists of a series of fluviatile sandstones interbedded with lacustrine mudstones, siltstones and shales which are underlain by the
Price River Formation and overlain by the Flagstaff Formation. The
North Horn is in transitional contact with the underlying Price River
Formation and the boundary between the two is difficult to set due to
extensive intertonguing. The transitional contact indicates an unbro-
ken progression from coarse-grained post-orogenic sandstones to
multi-colored mudstones, siltstones and shales as the highland source
areas were worn down.
The upper contact is conformable and generally is marked by
a change from the soft varicolored mudstones and shales of the North
Horn to the resistant red calcareous siltstones or green and gray
mudstones and shales of the Flagstaff Formation. However, in
Gooseberry Valley the argillaceous sediments of the North Horn For-
mation grade upward into the more resistant calcareous sediments
.
with no change in color. In the southern part of the area the contact
is gradational but the color changes abruptly from the red and brown
mudstones and shales of the North Horn to the green and gray shales
of the Flagstaff Formation.
Distribution and Topographic Expression.
The North Horn
Formation crops out widely in the Wasatch Plateau, Valley Mountain,
Gunnison Plateau, Pavant Range and in the Fish Lake Plateau. The
formation crops out extensively in the northern and central parts of
the mapped area and in isolated outcrops in the southern part. The
formation typically forms long slopes which are interrupted by resistant sandstones that form 10 to 30 foot cliffs. These resistant
34
sandstones cap prominent dip slopes and form cuestas which are distinctive features in Gooseberry Valley (Figure 10). In the north-cen-
tral and northeastern parts of the area the formation appears as a
thin veneer overlying the Price River Formation.
Lithology and Thickness.
Lithologically the North Horn For-
mation may be divided into two units: a lower unit, about 850 feet
thick, of alternating fluviatile and lacustrine deposits, and an upper
unit, about 350 feet thick, of even-bedded lacustrine deposits.
The lower unit is characterized by alternating fluviatile,
cross-bedded sandstones and lacustrine mudstones, siltstones and
shales. The sandstones are generally less than 25 feet thick but
locally attain thicknesses of 50 feet. The sandstones are lenticular
and display cut and fill structures (Figure 11). They are generally
light gray to tan in color, weathering to brown, yellow brown and
locally to white. The sandstones are dominantly fine- to medium-
grained in texture but locally are conglomeratic. They are generally
composed of sub-angular to sub-rounded, poorly sorted quartz grains
with minor amounts of black chert, and they are cemented by calcium
carbonate. Fresh samples from many of the beds are hard, but on
outcrop they are usually soft and friable due to solution of the carbonate cement. Though most of the sandstones are classified as quartz
arenites, thin-section analysis of two representative samples indicates a composition comparable to feldspathic arenites.
Conglomerate units within the formation are of minor importance. They are interbedded and gradational with coarse-grained
sandstones. One distinctive unit of pebble conglomerate, about ten
V
FIGURE 10.
Cuesta in the North Horn Formation at the northern end of Gooseberry Valley.
The section is formed of alternating beds of
varicolored sandstones and mudstones. Green
River beds on the skyline.
FIGURE 11. A channel formed in a finegrained sandstone unit near the base of the
North Horn Formation. The channel trends
in an west to east direction. Salina Canyon.
36
feet thick, crops out in the west-central part of the area, about one
half mile south of Gates Creek. The unit forms a dip slope about one
half mile long and one quarter mile wide. It is composed of rounded
pebbles of red, pink and white quartzite with subordinate clasts of dark
chert. The clasts are generally one to five centimeters in diameter
and are in a matrix of coarse-grained quartz and quartzite grains.
The conglomerate rests with slight erosional unconformity on an
underlying red siltstone unit and grades upward through fine pebble
conglomerate and conglomeratic sandstone to a red mudstone unit.
The conglomerate probably records an orogenic pulse in the source
area which caused the coarser material to be supplied to the site of
deposition.
The fluviatile sandstones alternate with even-bedded vari-
colored mudstones, siltstones and shales. These fine-grained units
are generally less than 25 feet thick where exposed, but covered
slopes, which appear to be formed on mudstone beds, indicate thicknesses of over 100 feet. These units are distinctively varicolored
and are red, brown, purple, or gray in color and are often mottled.
Their even-bedded nature and wide lateral extent suggest that these
fine-grained sediments are of lacustrine origin.
The upper unit, about 350 feet thick, is predominantly lacus-
trine and is similar to the North Horn Formation at its type locality
as described by Spieker (21, p. 132-135). The unit is best exposed
in Gooseberry Valley where it is composed of evenly-bedded red,
purple, brown, gray and mottled mudstones, siltstones, and shales
with a few interbedded yellow-gray to buff, fine- to medium-grained
37
sandstones. The sandstones are in part even-bedded and in part
cross -bedded, with some of the units showing channeling into underlying mudstone beds. They are 1 to 50 feet thick and are resistant,
forming prominent cuestas in Gooseberry Valley. Most of the sandstones appear to be of fluviatile origin but some may be lacustrine.
Spieker states that the North Horn Formation thickens to the
north and east and generally thins southwestward from 2, 500 feet in
the vicinity of Soldier Summit, on the north end of the Wasatch Pla-
teau, to about 500 feet in Salina Canyon (23, p. 26). In the mapped
area the North Horn Formation has a thickness of 1, 200 feet. How-
ever, three miles west of the mapped area, in Salina Canyon, the
formation thins and the upper part of the formation is observed to
lap out onto folded Early Cretaceous rocks which appear to have
formed an island within the lake in which the North Horn Formation
was deposited (23, p. 66).
Age. The section of varicolored fluviatile and lacustrine sandstones, mudstones and shales which comprise the North Horn Formation was originally defined by Spieker and Reeside (26) as the lowest
of three members of the Wasatch Formation of Eocene age. Originally the middle and upper members of the Wasatch Formation were
represented by what are now the Flagstaff Formation and the Colton
Formation respectively. Spieker (21, p. 120) states that the assignment of these three members to the Wasatch Formation was based on
fresh-water mollusks collected from the Wasatch Plateau, and on
structural relations, the Wasatch strata being deposited with angular
unconformity on older rocks folded during the Laramide orogeny.
38
This episode of orogeny was believed to mark the end of the Cretace-
ous Period.
In 1934 dinosaurian remains were collected from the basal
member of the Wasatch Formation in the vicinity of North Horn Moun-
tain, on the east flank of the Wasatch Plateau (21, p. 120). These
dinosaurian fossils indicated that the lowest member of the Wasatch
Formation was of Late Cretaceous rather than Early Tertiary age.
Spieker, in 1940, (21, p. 121) abandoned the name Wasatch Formation in this area and proposed the following revisions: 1) that the
original lower member of the Wasatch Formation be named the North
Horn Formation, 2) that the Flagstaff limestone member of the Wasatch Formation be given formational rank, and 3) that the name Colton Formation be adopted for the upper member of the Wasatch For-
mation. For a complete account of the revisions, refer to Spieker
(21, p. 120-121).
As now interpreted, the lower two thirds of the North Horn
Formation, is considered to be of Late Cretaceous age and contains
a Lance-type ceratopsian fauna (16). The upper one third of the for-
mation, as dated by mammalian fauna, is believed to be of Fort
Union age, which is early Paleocene. Within the mapped area the
only fossils found were abundant wood fragments which occur in many
of the fine-grained, cross-bedded sandstones.
Source Rocks and Depositional Environment. The clastic ma-
terials of the North Horn Formation appear to have been derived from
Early Cretaceous and older Mesozoic formations exposed to erosion
during the Late Cretaceous and Early Tertiary. Spieker (22, p. 78)
39
states that the red beds of the North Horn Formation were derived
from the erosion of pre-existing red beds. This relationship is demonstrated in parts of central Utah where beds of the North Horn For-
mation are deep red close to Jurassic and Triassic sources, gradually fading in color eastward away from the source. These relation-
ships are not seen in the thesis area, but the clean nature of the
quartz sandstones and the good degree of rounding of the detrital
grains suggest a source from pre-existing sedimentary units. Sixtyfive measurements of foreset cross-laminations from fluviatile sandstones at six localities do not indicate a specific source direction but
suggest a source from the west (Figure 5). Channel deposits observed
within the formation suggest a predominant west to east direction of
transport.
The cross-bedded sandstones with cut and fill structures
which alternate with varicolored siltstones, mudstones and shales of
wide lateral extent suggest alternating conditions of fluviatile and
lacustrine deposition. The varicolored facies are a function of environmental conditions and indicate the deposition of heterogeneous
clastic sediments including much red and other brightly colored ma-
terial under oxidizing conditions on a terrain of low relief. The
sharp changes from the even-bedded siltstones and mudstones to
fluviatile sandstones and conglomerates attest to recurring positive
movements in the source areas, These recurring positive movements periodically caused the streams to supply coarse material which
temporarily invaded the basins in which the varicolored lacustrine
40
sediments were being deposited.
Flagstaff Formation
The Flagstaff Formation was first described in the Wasatch
Plateau by Spieker and Reeside (26). The unit was originally given
member status and consisted of that fresh-water limestone section
that is consistently present between the upper and lower varicolored
members of the former Wasatch Formation. The terminology was
later revised and the unit was given formational status (21, p. 120).
The only complete exposure of the Flagstaff Formation within
the area mapped is west of Gooseberry Creek (Figure 12) in the ex-
treme northwestern part of the region (Plate 3). At this locality the
formation is bounded above and below by conformable contacts with
the Colton and North Horn Formations respectively. The contacts
are gradational in nature; the varicolored, lacustrine shales and
mudstones of the Colton and North Horn Formations grade into the
red calcareous beds of the Flagstaff.
In Gooseberry Valley there
is no change of color between the formations above and below but in
the southern part of the area there is an abrupt change from the red
beds of the North Horn Formation to the grays and greens of the
shales and mudstones which occur at the base of the Flagstaff Formation. In this southern area the Flagstaff is usually overlain un-
conformably by Tertiary lavas, but at one locality, sec. 11, T. 24 S.,
R. 2 E., the Flagstaff is overlain by the Colton (?) Formation.
Distribution and Topographic Expression. The Flagstaff Formation crops out extensively in central Utah. Exposures occur in
FIGURE 12. Red Flagstaff (left center) overlying
west dipping varicolored North Horn beds in Gooseberry Valley. This is the only complete section of
the Flagstaff exposed in the area. Green River beds
on the skyline.
42
the Valley Mountains, Pavant Range and in the Gunnison, Wasatch
and Fish Lake Plateaus. The formation is one of the most prominent
cliff-formers in the Wasatch Plateau and because of its regional per-
sistence is an excellent marker unit.
South of Salina Canyon, the Flagstaff has largely been removed
by erosion and crops out in limited exposures. The only complete
section is exposed west of Gooseberry Creek (Plate 3) where the formation forms a prominent cliff about 80 feet in height. Three miles
west of the mapped area, in Salina Canyon, this section thins and laps
out on a topographic high that formed an island in the Flagstaff lake
(23, p. 87). In the central and southern parts of the district the formation generally crops out in limited and isolated exposures where
it has been preserved from erosion in down-dropped fault blocks and
later disturbed by extensive landsliding. The most complete section
in this area is exposed on the west side of Niotche Creek, in sec. 35,
T. 23 S., R. 2 E. , where the formation forms a 300 foot cliff.
Lithology and Thickness.
The Flagstaff Formation is com-
posed of limestones, shales, mudstones, siltstones and sandstones
which locally become conglomeratic. There are two distinct lithologic types found within the region. In Gooseberry Valley the forma-
tion is a red colored cliff-former and is composed of red argillaceous
limestone, calcareous siltstone and a few beds of sandstone. In the
central and southern part the formation consists predominantly of
white and gray limestone interbedded with green mudstone and a few
sandstone beds.
The sandstones of the Gooseberry Creek section are yellow,
43
brown and red when fresh and weather to a light brown and gray.
They are composed of fine- to medium-grained quartz grains which
are sub-rounded to rounded and are cemented by calcium carbonate.
The sandstones are massive to irregularly-bedded and generally occur
in beds from 5 to 20 feet thick. The beds commonly contain lenses of
gray and yellow gray siltstone and are interbedded with mudstone,
siltstone and limestone. Where the sandstones are in contact with
siltstones the boundary between them is gradational; however, where
the sandstones are in contact with mudstones or limestones the contacts may be either gradational or sharp.
The limestones in the Gooseberry Creek section are dark red,
purple, and light gray in color and occur in massive beds less than
two feet thick. The limestones contain a high percentage of argillaceous material and they grade into calcareous mudstones and siltstones.
The argillaceous sediments are gray, red, brown, purple, and mottled. They are both even- and irregularly-bedded and occur in beds
between one and five feet thick. The argillaceous sediments grade
into one another and into the interbedded limestones and sandstones.
In the south-central and extreme southern parts of the area
the Flagstaff crops out in small limited exposures and the complete
section is nowhere exposed. The thickest section exposed is on the
west side of Niotche Creek (Plate 3). At this location the formation
is composed predominantly of gray to white limestones intercalated
with thin-bedded gray and green shales and mudstones. A few crossbedded sandstones are present. The limestones are micritic contain-
ing large amounts of clay-size material. Some beds have been partly
44
replaced by chert. The limestones are both evenly-bedded and irreg-
ularly-bedded and occur in thin, one half to one inch, discrete beds
which form three to five foot thick intervals. These limestone intervals are interbedded with 8 to 12 inch layers of light gray calcareous
mudstone and shale and form units as thick as 50 feet.
The mudstones and shales are gray, grayish green and brown
in color and occur in beds ranging in thickness from a few inches to
50 feet. The thinner units are intercalated with the limestones and
the thicker layers separate the thick limestone units.
Only two sandstone units occur in this sequence. One is less
than a foot thick and the other is about 50 feet thick. The sandstones
are brown to red in color and are cross-bedded. They are composed
of fine- to medium-grained, sub-angular to sub-rounded quartz and
chert grains which are weakly cemented with calcium carbonate. The
thick unit of sandstone becomes intricately intercalated with siltstone
about 20 feet above the base and is predominantly green siltstone in
the upper ten feet.
About 1. 5 miles south of the Niotche Creek section is another
isolated outcrop of the Flagstaff Formation (Plate 3). The outcrop
is at least 50 feet thick and forms a rounded hill. The exposed section is composed predominantly of limestone but contains intercalated
siltstone and mudstone (Figure 13). The section does not correlate
lithically with any of the other exposed sections. The limestones
are micritic and contain a high proportion of argillaceous material.
Chert is a common constituent and may replace as much as 50 percent of some limestone beds.
FIGURE 13. An outcrop of the Flagstaff Formation composed of thin- to medium-bedded lime-'
stone intercalated with thin units of mudstone and
shale. Near Salina Reservoir.
46
Because the carbonates are noticeably argillaceous acid residue analyses were made of two samples (JBA-46, JBA-87) from this
locality in an attempt to determine the amount and composition of the
detrital material. These analyses indicate a clay-size fraction of
30 percent by weight for sample JBA-46 and 16 percent for sample
JBA-87. Petrographic studies of the insoluble. residue suggest that
the'ar,gillaceous fraction is composed of cryptocrystalline silica.
X-ray analysis of the residue from 'sample JBA-46 also suggests the
presence of cryptocrystalline silica.
The limestones at this locality are interbedded with dark gray
and green evenly-bedded siltstones and mudstones which range in
thickness from a few inches to 15 feet. Some of the contacts are
gradational but in some cases the contacts between the limestone and
overlying siltstones are sharp.
Another outcrop, in sec. 12, T. 24 S., R. 2 E., (Plate 2),
is significant because the base of the formation is exposed. The red
mudstones and sandstones of the underlying North Horn Formation
give way to slopes covered by flaggy, micritic and cherty limestone
and green siltstone and mudstone. The section is about 100 feet in
thickness and is composed predominantly of green siltstone and mudstone. Interbedded with the mudstones are a few thin beds of lime-
stone, not exceeding five feet in thickness, which crop out as thin
ridges on the steep slope formed on the weaker argillaceous rocks..
The individual beds are one half to one inch in thickness. Near the
top of the section, which is overlain unconformably by Tertiary
volcanics, is a 15 to 20 foot outcrop of cross-bedded sandstone.
47
The sandstone is light green to gray when fresh and weather to light
green. The sandstone unit is composed of fine- to coarse-grained,
sub-angular quartz grains and a few rock fragments and is cemented
by clay and calcium carbonate. The contact relations between the
various lithologies of the section are obscured because of limestone
and mudstone float which covers the surface.
In the southern part of sec. 11, T. 24 S. , R. 2 E. , the upper
part of the Flagstaff Formation is exposed. The lithology changes
abruptly from a sequence of limestones and mudstones to one of peb-
ble conglomerate. The contact is concealed but the pebble conglom-
erate. The contact is concealed but the pebble conglomerate is believed to be the basal part of the Colton Formation in this area. The
Flagstaff at this locality is composed of white to cream colored beds
of cherty, micritic limestone which do not exceed five feet in thickness and are interbedded with units of green mudstone ranging from
10 to 20 feet in thickness. The limestones occur in discrete, fissile
beds about one quarter to three inches thick and crop out as thin resistant ridges in slopes formed on the mudstone units. The contacts
between the limestone and mudstone units are sharp where they can
be observed. The exact thickness of the exposed section cannot be
determined because of slumping at the base of the outcrop, but it is
at least 100 feet thick.
X-ray analyses were made of two samples of carbonate ma-
terial from outcrops of the Flagstaff Formation in the south-central
part of the area. The analyses, made by Mr. Tracy Vallier of the
Oregon State University Geology Department, indicated that the two
48
samples are composed of nearly 100 percent dolomite.
Thin-sections
of the samples were prepared and studied with a petrographic micro
scope. No textures which would suggest that the dolomite had been
formed by the replacement of limestone were observed. The samples
fit Folk's description
(6, p. 14) of a dolomicrite. Further studies
are necessary to determine the origin of the dolomites but the writer
believes that they may be of primary origin. Graf et al, (7) report
unlithified magnesium carbonate deposits in the Great Salt Lake and
believe that they were formed by chemical precipitation or by diagenetic
alteration. Alderman and Skinner (1), in studies of dolomitic
sediments in some lake deposits in southeast Australia, conclude that
the dolomite is a primary precipitate. As only two samples were
analysed the writer does not know how many of the limestone units,
described within the Flagstaff Formation, are actually composed of
dolomite.
Age. On the basis of molluscan faunas collected by La Rocque,
the age of the Flagstaff is suggested to be Late Paleocene for the low-
er part and Early Eocene for the upper part (13, p. 140-141). F. M.
Swain (28) collected ostracods from the base of the red Flagstaff section exposed west of Gooseberry Creek.
These suggest that the base
of the formation was correlative with the upper Colton or lower Green
River Formations of the Uinta Basin. This would indicate a late
Early Eocene age for the base of the formation. McGookey (16) be-
lieves that the Flagstaff beds along Gooseberry Creek can be physical-
ly traced to the part of the section identified by La Rocque as Paleocene.
It is not known if the top of the formation is of Paleocene age
49
or if it is of Eocene age as is the case in the Wasatch Plateau (14, p.
73). The exposures near the top of the Flagstaff Formation in the
southern part of the mapped area are lithologically similar to the up-
per units of the Flagstaff found in the Wasatch Plateau. The latter
have been dated as Eocene in age by La Rocque.
Source Rocks and Depositional Environment. The limestone
and limy argillaceous units within the Flagstaff Formation, as well
as the field relations, indicate deposition in a lacustrine environment.
La Rocque (14, p. 11) states that the Flagstaff Formation of central
Utah was deposited in a shallow lake of great extent which covered a
minimum area of 2, 800 square miles and possibly a maximum area
of 7, 000 square miles.
The predominantly red argillaceous limestones, calcareous
shales and mudstones, and sandstones which comprise the red Flagstaff section in Gooseberry Valley suggest deposition near the edge
of the Flagstaff lake where the supply of detrital material was high.
The red color of the detrital material suggests that the sediments
were derived from the red beds of pre-existing Cretaceous and Jurassic units which cropped out along the edge of the lake. Rocks of
this type occur three miles west of the thesis area where the red
Flagstaff section thins over folded Late Jurassic and Late Cretaceous
beds which formed an island in the Flagstaff lake (Figure 14).
The dense micritic limestones alternating with limy shales
and mudstones which are characteristic of the formation in the south-
ern and central parts of the area suggest deposition farther from the
shore of the lake. Mud cracks and ripple marks found within the
5
FIGURE 14. Three miles west of the mapped
area the nearly horizontal Flagstaff Formation
laps out westward on east dipping strata of the
Indianola Group.
51
limestone units indicate that the lake was shallow and that the lake
bottom was at times exposed to the atmosphere. A few medium- to
coarse-grained cross-bedded sandstones which occur locally within
the formation indicate deposition in a high energy environment, pos-
sibly analogous to a paralic environment.
The alternation of the limestones and limy argillaceous units
which are characteristic of the Flagstaff Formation in the central and
southern parts of the area has been explained by La Rocque (14, p.
78) as the result of changes in the depth of the lake rather than
changes in the supply of sediment to the basin. These changes in
depth were brought about by small periodic movements on faults
which are believed to have existed in and around the lake basin. The
dense micritic nature of the limestones suggests precipitation of calcium carbonate from solution (14, p. 78). The calcium carbonate
was probably brought into the lake basin by streams which drained
areas adjacent to the lake. Some finely brecciated limestones were
observed within the Flagstaff and suggest that some of the limestones
were produced by plants. Pettijohn (18, p. 410) states that plants
such as Chara precipitate calcium carbonate on their leaves and
stems and that these deposits when sloughed off collect on the lake
bottom. Limestones formed in this way are characterized by a
pseudobrecciation produced by small angular chips or flakes of cal-
cium carbonate embedded in a fine-grained matrix of similar composition. Float on one outcrop of Flagstaff limestone yielded what
appear to be fragments of algal growths that have been silicified.
No algal growths were observed in place.
52
Colton Formation
The Colton Formation was first defined by Spieker and Reeside
(26) to be the upper member of the Wasatch Formation and was later
redefined by Spieker (21, p. 139) and given formational rank. The
type locality is in Price Canyon, two miles east of Colton, Utah. The
type section consists of 1, 500 feet of irregularly-bedded gray sand-
stone, greenish buff sandstone, and deep red to varicolored shale,
all of fluviatile origin. In the mapped area the formation consists of
about 500 feet of evenly-bedded brownish red shales, mudstones and
siltstones which are intercalated with mottled gray and purplish gray
mudstones. In contrast to the type section there is no evidence of
fluviatile deposition and the formation appears to be of lacustrine
origin.
The only complete section of the Colton Formation is located
on the west side of Gooseberry Valley in the northwestern part of the
area (Plate 3). At this locality the formation lies between the overlying Green River and the underlying Flagstaff formations. The con-
tacts are gradational in nature; the lacustrine shales and mudstones
of the Colton grade into the red calcareous beds of the Flagstaff below
and into the grayish green shales and mudstones of the overlying
Green River Formation (Figure 15).
Distribution and Topographic Expression. Westward and
southward from the type locality the Colton Formation is exposed
along the west edge of the Wasatch Plateau, in the Gunnison Plateau,
the Valley Mountains, and in the northwestern part of the Fish Lake
FIGURE 15. A view to the northwest from the center
of Gooseberry Valley showing the gradational contact
between the varicolored mudstones of Colton Formation and the overlying green mudstones of the Green
River Formation. Strata of the Colton Formation
form the slopes at the base of the cliff and underlie
the valley in the foreground.
54
Plateau; elsewhere it has been removed by erosion. The only prominent exposures of the Colton within the mapped area are on the west
side of Gooseberry Valley where the formation lies at the base of a
cliff formed by the Green River Formation. The formation is nonresistant and forms part of the valley floor. The outcrop is continuous
along the west side of the valley until it becomes covered by alluvium
and landslides about four miles south of Utah Highway 10.
Isolated outcrops of the Colton (?) Formation occur south of
the Gooseberry Creek Ranger Station where it has been preserved in
fault blocks (Plate 3). Extensive landsliding obscures the contacts
with adjacent outcrops of the Flagstaff and Green River formations,
but these isolated sections of the Colton Formation are lithologically
similar to those found in Gooseberry Valley. In the extreme south
central part of the area (Plate 3) a discontinuous section of varicolored conglomerates, sandstones and siltstones, which lies between
the Flagstaff Formation and overlying Tertiary volcanics, has been
assigned to the Colton Formation. The contact relations with the
underlying Flagstaff Formation are concealed and an erosional un-
conformity separates the overlying Tertiary volcanics from the Colton Formation.
Lithology and Thickness.
The Colton Formation is typically
composed of even-bedded brownish red mudstones and siltstones that
are generally mottled with patches of gray and purple. A few thin
beds of shale, sandstone and limestone are present at some localities.
A conglomerate and sandstone unit overlies the Flagstaff Formation
in sec. 11, T. 24 S., R. 2 E. and is believed to be part of the Colton
55
Formation.
Mudstones and argillaceous siltstones are the predominant
rocks of the formation. They are generally brownish red to gray, are
mottled with patches of grayish yellow, gray and purple, are evenlyto unevenly-bedded, and occur in units ranging from a few inches to
over 100 feet in thickness. The siltstones and mudstones grade into
each other and into the interbedded sandstones.
The sandstones are gray, yellow gray to grayish green and
weather to shades of light brown. They are evenly-bedded and occur
in one eighth to one half inch beds which form units ranging in thick-
ness from one to three feet. The sandstones are fine-grained and are
composed predominantly of sub-angular to sub-rounded, well-sorted
quartz grains weakly cemented by calcium carbonate. The units are
gradational with the enclosing siltstones or mudstones.
The conglomerate and sandstone unit which overlies the Flag-
staff Formation in the extreme south-central part of the area ranges
in thickness from 0 to 40 feet, the variation a result of erosion. The
unit is yellow brown, brown and orange and weathers to shades of
dark red brown and dark gray. The clasts of the conglomerate are
sub-rounded to well-rounded and range in size from 0.2 cm to 7. 5
cm though most are between 1 and 3 cm. in diameter. The clasts
are 75 percent light colored quartzite and 25 percent dark quartzite,
chert and argillite. They are weakly cemented by a dark brown matrix of coarse sand and grit containing clay and iron oxide. Inter
bedded with the conglomerates are sandstones ranging in thickness
from six inches to six feet. They are composed mainly of fine- to
56
coarse-grained quartz grains and are cross-bedded and friable
(Figure 16). They are the same color as the enclosing conglomerate
beds and are gradational with them. Within one-quarter mile along
strike the conglomerate and sandstone unit reaches a maximum ob-
servable thickness of 40 feet and the color changes from dark red
brown to light gray. This is a function of a change in the matrix as
the clasts remain the same. It appears to be caused by a marked
decrease in the iron oxide content of the matrix. At this locality the
conglomerate and sandstone unit is overlain by at least 30 feet of
gray siltstone containing beds of sandstone which grade into red
argillaceous siltstone and mudstone. The two units are separated by
a minor erosional unconformity and the entire sequence is overlain
unconformably by Tertiary lava. This unconformable contact is un-
dulating and it appears that the volcanics were extruded on an erosional surface of considerable relief. The contact between the Colton (?)
beds and the underlying Flagstaff Formation is obscured but it appears
to mark a disconformity. This is based on the observation that the
contact seems to undulate and that the beds above and below the con-
tact are parallel. It is believed that the contact marks a minor erosional unconformity.
These conglomerates and sandstones cannot be correlated
lithologically with any other units within the area but because of
stratigraphic position the unit is believed to be a part of the Colton
Formation. Because of the limited exposures and the fact that the
upper part of the unit has been eroded away it cannot be determined
if the conglomerate and sandstone unit is correlative with the upper
FIGURE 16. An outcrop of the
Colton (?) Formation composed
of cross-bedded sandstones with
thin beds of conglomerate.
58
or lower part of the Colton Formation exposed in Gooseberry Valley.
More detailed mapping might indicate that the unit belongs to one of
the later Tertiary formations which crop out to the west of the mapped area and have been described by McGookey (16). However, at
present the unit in question does not compare with the published
descriptions of these later Tertiary formations.
In thickness the Colton Formation ranges between 1, 500 feet
at the type locality and zero feet where the formation loses its iden-
tity by intertonguing with the Green River Formation west of Soldier
Summit in the northern part of the Wasatch Plateau (23, p. 34). As
a rule, however, it is between 300 and 1, 000 feet thick. Within the
mapped area the formation is 530 feet thick where the complete section is exposed in Gooseberry Valley. In other exposures within the
area only part of the formation is exposed and none of the sections
are over 100 feet thick.
Age. Ostracods collected from the Colton Formation in
Gooseberry Valley and identified by Swain (28) suggest a correlation
with the uppermost Colton or lower Green River of the Uinta Basin.
This indicates an early to middle Eocene age for the formation.
Fresh water mollusks collected in the Wasatch Plateau were identified by Reeside (21, p. 139) as members of the traditional Wasatch
fauna. It appears that an early Eocene age designation for the for-
mation in the thesis area is permissible but Spieker (21, p. 139)
states that because of the lack of diagnostic vertebrate fossils the
Eocene designation is not completely supported by fossil evidence.
A sample of limestone collected from the Gooseberry Valley section
59
of the formation contains some ostracod fossils. The age of these
fossils was not determined by the writer.
No other fossils were
collected.
Source Rocks and Environment of Deposition.
In the type area
Spieker has described lithologies which represent deposition in floodplain and channel environments but within the mapped area lithologies
of this type were not observed. The predominance of even-bedded
argillaceous units and the interbedded limestone units containing
fresh water ostracods indicate that the Colton Formation was depos-
ited in a lacustrine environment. A cross-bedded conglomerate and
sandstone unit that has been described from one locality appears to
indicate that fluviatile conditions existed at least locally within the
basin of deposition.
This unit may represent deltaic deposition near
the margin of the lake or it may record a pulse of orogeny in areas
adjacent to the site of deposition and a temporary supply of coarse
debris.
Green River Formation
The Green River Formation was named by Hayden (10, p.
89-92) for outcrops near Green River, Wyoming. Bradley (3, p. 9)
later described the type section in greater detail. At the type local-
ity the formation consists of finely laminated marlstones, limy and
sandy shales, and oil shales. In central Utah the Green River Formation differs both from the rocks at the type locality and from the
well known facies of the Uinta Basin and western Colorado. In the
thesis area the formation consists of two members, a lower
60
green-gray to light green shale and an overlying unit of cream to tan
limestone. In central Utah the formation is transitional with the
underlying Eocene Colton Formation and is overlain unconformably
by the Crazy Hollow Formation (23, p. 36). The lower contact is
well exposed within the mapped area but the overlying Crazy Hollow
beds have been removed by erosion. McGookey (16) has described
the upper contact from areas immediately west of the thesis area.
He states that the Green River Formation wedges out south of Goose-
berry Creek in T. 23 S., R. 2 E. due to differential uplift and erosion
that took place prior to the deposition of the Crazy Hollow beds. The
fluviatile varicolored clastic beds of the Crazy Hollow Formation
were deposited disconformably over the eroded Green River limestones and older beds.
Distribution and Topographic Expression. In central Utah the
Green River Formation is exposed at the base of the north and west
flanks of the Wasatch Plateau, in the Gunnison Plateau, Valley Moun-
tains and Pavant Range, and in the extreme northern part of the Fish
Lake Plateau. Within the mapped area the formation crops out along
the western side of Gooseberry Valley (Figure 15). The outcrop extends south from Utah State Highway 10 to the southern edge of T. 23
S. , R. 2 E. where it wedges out. In other parts of the area the for-
mation has been removed by erosion except for one isolated outcrop
in sec. 28, T. 23 S. , R. 2 E. where it has been preserved in a fault
block. Typically the formation is an impressive cliff-former and
forms the western boundary cliff of Gooseberry Valley. The upper
part of the cliff is nearly vertical and is formed by the resistant
61
upper limestone member of the formation. The lower shale member
forms a steep slope beneath the limestone cap.
Lithology and Thickness. The Green River Formation in the
mapped area consists of two members: a lower green to grayish
green mudstone and shale member and an upper white to tan limestone
member. The lower member, about 430 feet thick, is composed
mainly of green to grayish green mudstones and shales but contains
many thin layers and lenses of limestone, siltstone, and sandstone.
The mudstone and shale beds are evenly-bedded and form units rang-
ing from 5 to 125 feet in thickness. Thinner units are composed
entirely of shale or mudstone but the thicker units contain thin inter-
bedded limestones, siltstones and sandstones. The sandstones range
in thickness from three to ten feet and are finely cross-bedded. Some
units are conglomeratic at their base and contain small pebbles of the
underlying mudstones and limestone. Generally the sandstones are
fine- to medium-grained and are composed of sub-angular to sub-
rounded quartz grains cemented by calcium carbonate. Some of the
contacts are sharp but others are gradational, both above and below,
from sandstone into siltstone and mudstone. The interbedded silt-
stones are grayish green in color and generally less than one foot in
thickness. They are usually cemented by calcium carbonate and
contain small ferruginous concretions which are less than 1 cm. in
diameter. The siltstones have gradational contacts with the adjacent
sandstones and mudstones. The interbedded limestones range in
thickness from 3 to 12 feet and are white to gray in color. The
limestones are dense and resistant and form minor ledges on the
62
steep mudstone and shale slopes.
The upper limestone member, of which about 300 feet is ex-
posed in the mapped area, is characterized by both thin-bedded platy
limestone and massive dense limestone that locally is oolitic. The
thin-bedded limestones, which are the most common, are white to
light brown in color and occur in discrete one to three inch beds
which are fissile. The massive limestones are also white to light
brown in color and occur in beds ranging from a few feet to over 100
feet in thickness. These limestones are especially resistant because
of partial to locally complete replacement by chert.
Age. McGookey (16) reports that ostracods collected from
limestones near the top of the Green River Formation in Soldier Canyon, four miles west of the mapped area, have been identified by F.
M. Swain and indicate a correlation with the middle part of the Green
River Formation of the Uinta Basin. Bradley (3, p. 9) considers the
Green River Formation of Wyoming and northeastern Utah to be of
middle Eocene age. Inasmuch as the fossil assemblages found in the
vicinity of the mapped area correlate with those described by Bradley there seems to be no doubt that, in this area, the Green River
Formation is of middle Eocene age.
Source Rocks and Depositional Environment. The limestones,
the even-bedded shales and mudstones, and the fresh water fossils
found within the Green River Formation indicate deposition in a lacustrine environment. Bradley (3, p. 54), who has studied the Green
River deposits in northeastern Utah and Colorado, pictures the lake
as a broad sheet of water flooding a large plain on which the Colton
63
Formation was being deposited, and enclosed by mountains or high
hills. The depth of the lake near the shore was not more than 10 or
15 feet and the deepest part of the basin was 50 or 60 feet deep and
may have been as deep as 75 to 100 feet.
West of the thesis area McGookey (16) has reported biostromal
growths of Chlorellopsis coloniata in the massive limestone units and
indicates that this alga grows in water depths of less than 15 feet.
The factors which determine the precipitation of the carbonates, both
organic and chemical, are outlined in detail by Bradley (2, p. 641 643).
The presence of lensing cross-bedded sandstones, some of
which are conglomeratic and contain wood fragments, in the lower
mudstone and shale member of the formation indicates deposition in
a sub-aerial or shallow water high energy environment.
The limestones and argillaceous rocks are considerably dif-
ferent from the marls and oil shales which are characteristic of the
Green River Formation in the Uinta Basin and in Colorado. This
difference is either a function of the faunal productivity of the lake
in this area or the lack of that thermal or chemical stratification
which induces reducing conditions on lake bottoms and is a pre-
requisite for the preservation of organic material.
The large accumulation of carbonates and argillaceous ma-
terial was mainly a function of the available source areas. Harris
(9), discussing Mesozoic positive areas in western Utah, states that
thrust faulting during the Late Cretaceous exposed Paleozoic and
Early Mesozoic carbonates and clastic rocks in areas west of the
present Sevier Valley. Post-thrusting erosion supplied fine
64
sediments to the fresh water lakes of Central Utah where they were
deposited as calcareous and argillaceous beds.
Gray Gulch Formation
Within the mapped area the Gray Gulch Formation is the next
higher stratigraphic unit after the Green River Formation because
the Crazy Hollow Formation, which lies between them in areas to
the west (16), is not exposed.
The lacustrine tuffaceous sediments which unconformably
overlie the Crazy Hollow Formation in the Salina district were provisionally named the Gray Gulch Formation by Spieker (23, p. 37-38).
No type section was named but McGookey (16) indicates that Spieker
had in mind a section in Crazy Hollow (sec. 32, T. 21 S., R. 1 E.).
McGookey proposes subdividing the unit into two distinct formations:
1) The "Bald Knoll Formation" would be the lower part of the Gray
Gulch Formation, and would consist of evenly-bedded light gray to
white shale, some of which is bentonitic; 2) The "Dipping Vat Forma-
tion" would be the upper coarse interval of the Gray Gulch Formation
and would include evenly-bedded tuffaceous sandstones that contain
varying amounts of glass and other pyroclastic fragments interbedded
with white clay and silty limestone. Because of limited exposures
of the Gray Gulch Formation within the mapped area the writer has
not attempted to subdivide the formation. However, comparisons of
type sections and written descriptions indicate that the outcrops
within the area are correlative with McGookey's "Dipping Vat For-
mation''.. Spieker (23, p. 38) states that the formation is bounded
65
above and below by erosional unconformities, but the contacts are
concealed within the mapped area.
Distribution and Topographic Expression. McGookey (16)
and Spieker (23, p. 37) have correlated the Gray Gulch Formation
with strata exposed in the southern Wasatch Plateau, Pavant Range,
Gunnison Plateau, Tushar Mountains and possibly in Iron County in
southwestern Utah. Within the mapped area exposures are limited
to a few outcrops in the south-central part of T. 23 S. , R. 2 E. The
strata are resistant and form minor cliffs 20 to 40 feet high (Figure
17) which stand out from landslide areas. At one location a resistant
limestone forms a minor dip slope.
Lithology and Thickness. Within the mapped area the Gray
Gulch Formation consists of interbedded limestones, shales, siltstones and sandstones. The limestones are white to dark gray in
color and weather to white and gray and in some cases to light brown.
They are even-bedded and occur in beds one-eighth totwo inches thick
which form units less than two feet thick. They are both micritic and
fossiliferous. One dark gray limestone unit contains abundant gas-
tropod tests and exudes a fetid odor when struck by a hammer. The
limestones are sharply separated from the interbedded clastic sediments and are resistant to erosion, forming thin ledges in otherwise
steep slopes.
A few reddish brown, thinly-laminated shales are present
and occur in units about six feet thick. The shales are gradational
with the interbedded siltstones but are sharply defined from the sandstone units. The siltstones are light brown in color, are evenly-
FIGURE 17. An outcrop of interbedded limestone, shales, mudstones and tuffaceous sandstones of the Gray Gulch Formation.
67
bedded, occur in discrete one-half inch beds, and form units ranging
from two to four feet in thickness. The siltstones are gradational
into interbedded shales and sandstones.
The sandstones are tuffaceous, are gray to white in color and
weather to reddish brown. They are both massive and finely crosslaminated and occur in units ranging in thickness from a few inches
to four feet. They are coarse- to medium-grained, poorly sorted
and are composed of angular- to sub-angular grains of dark gray
chert, quartz, and rock fragments in a matrix of glass shards and
clay. They are classified as volcanic sandstones. Some of the sandstones are conglomeratic at their bases and include pebbles of the
underlying shale and silt stone units.
McGookey (16) has measured a section of the Gray Gulch Formation immediately west of the mapped area and reports a thickness
of over 1, 250 feet for the formation. Within the mapped area the
isolated outcrops have been disturbed by faulting and landsliding this
-thickness is not representative of the actual thickness of the formation.
Age. McGookey (16) states that Charophytes collected from
the lower part of the formation were tentatively determined to be of
a late Eocene or Oligocene age. Gastropods of the family Lymnaeidae
and ostracods of the genus Heterocypris collected from the upper
part of the formation suggest a correlation with the uppermost Green
River or Uinta formations of the Uinta Basin. These facts suggest
a late Eocene and possibly an early Oligocene age for the formation.
Planorbid gastropod fossils were collected by the writer but were
,.
68
not identified.
Source Rocks and Depositional Environment. The limestones,
the presence of fresh water fauna, and the even-bedded nature of the
fine-grained sediments indicate that the formation was deposited
under lacustrine conditions. Charophytes, reeds, air-breathing
gastropods and algae, reported by McGookey in areas adjacent to
the mapped area, indicate that the lake in this area was very shallow
during part of its history. The interbedded finely cross-laminated
sandstones and conglomeratic sandstones also indicate sub-aerial or
shallow water high energy conditions. The size of the lake in which
the formation was deposited is not known but considering the known
extent of the outcrops it appears to have been smaller than the Uinta
Lake in which the Green River Formation was deposited.
The fine-grained nature of the clastic sediments and the interbedded limestones suggest that the sedimentary materials were de-
rived from pre-existing sedimentary rocks. The high percentage
of tuffaceous material within the clastic sediments and particularly
within the sandstones indicates that volcanic activity had been initiated in areas adjacent to the basin of deposition. Neither the direction nor the distance to the volcanic source areas could be determined
by studying the few exposures of the formation that are present with-
in the area studied.
Tertiary Lavas
The Tertiary lavas exposed in the thesis area represent the
northern edge of a great mass of flows which covers more than
69
3, 000 square miles of the High Plateaus of Utah. The extrusives
within and adjacent to the area were first studied by Dutton (5, p.
265) in the late 1870's and he mapped them as II ... 700 feet of horn-
blendic trachytes in massive sheets alternating with augitic andesites,
which are much thinner." McGookey (16) has applied the term
"Bullion Canyon volcanics, lava flows" to the sequence of extrusives
because they appear to be correlative with a sequence of Early Ter-
tiary tuffs, volcanic breccias, and latite flows that are exposed near
Marysville, Utah, and which have been named the "Bullion Canyon
volcanics". Because the lavas were not studied in detail by the
writer there has been no attempt to subdivide the extrusive volcanic
rocks exposed in the mapped area or to correlate them with other
volcanic rocks in adjacent regions. The volcanic rocks have been
deposited on an erosional surface of considerable relief and overlie
sedimentary rocks of Early Tertiary age.
Distribution and Topographic Expression. The lavas within
the area are part of a volcanic cover which extends over 80 miles
to the south. At present the flows are continuously exposed across
the southern part of the area (Figure 18). It is possible that they
originally extended north into the southern part of the Wasatch Plateau, and that they were subsequently removed by erosion. Spieker
(23, p. 38) states that the northern-most lobe of the lava fields of
the central High Plateaus extends a few miles into the foothills of the
Wasatch Plateau in the vicinity of Salina, Utah. The sequence of
lava flows in the southwestern and southeastern parts of the mapped
area forms nearly vertical cliffs over 300 feet high rising above
aol
FIGURE 18. A view south from near Salina Reservoir
toward the cliff and steep talus slope formed by Tertiary lavas.
71
steep talus slopes. In the central part of the region the volcanic cover
is much thinner and the flows cap steep slopes formed on Late Cre-
taceous and Early Tertiary sedimentary rocks. In the east-central
part of the area the volcanic cover has been preserved in a fault
block, the UM Plateau (Plate 2), and forms a steep cliff over 300 feet
high. The surface of the lava-covered plateau in the extreme south-
ern part of the area is one of very low relief and slopes gently to the
south.
Lithology and Thickness. The Tertiary volcanics are com-
posed predominantly of lava flows. In sec. 34, T. 23 S., R. 2 E.
some tuffaceous sandstones and pumice tuffs are exposed at the base
of the lava sequence. These probably correlate with McGookey's
(14) "Bullion Canyon volcanics, clastics". This unit includes mudflows, conglomeratic tuffaceous sandstones and tuffs that discon-
formably overlie the Gray Gulch Formation in areas west of the
mapped area. The tuffaceous sediments were not mapped as they
are exposed at only one locality and have been disturbed by landsliding.
The flow rocks are dark bluish black to light gray and weather
to light gray, dark brown and pinkish brown. The flows range in
thickness from a few feet to over 40 feet. Individual flows can be
discerned by changes in color and texture. Some of the flows are
massive and others contain flow lines and vesicles which are elongated in the direction of flow. Four rock samples were collected
and sectioned. The rocks examined, on the basis of the phenocrysts,
may be classified as augitic andesites. Andesine and augite are the
72
predominant phenocrysts and iddingsite, as pseudomorphs after
olivine, is a common accessory mineral. There are probably other
kinds of rocks in the flows that were not sampled as Dutton (5) has
classified the flows as trachytes with subsidary augitic andesites and
McGookey (14) reports the presence of andesites and latites.
The thickness of the volcanic sequence within the thesis area
is difficult to determine because the base is covered by talus slopes,
rock glaciers and landslide debris. In general it appears that the
unit ranges in thickness from less than 50 feet in the south central
part of the area to over 700 feet in the southeastern and southwestern
parts of the area. The differences in thickness across the southern
part of the area are due to: 1) extrusion on a surface of relief, 2)
faulting which has protected parts of the unit from erosion, and 3)
subsequent erosion which has modified the surface of the volcanic
sequence. McGookey (14) indicates that in areas south and east of
the mapped area the volcanics attain thicknesses in excess of 1, 000
feet.
Ajae. The extrusive rocks of the northern part of the Fish
Lake Plateau unconformably overlie Late Eocene sedimentary rocks
and pre-date the period of pediment development in the region. They
also pre-date the Late Tertiary normal faulting which was probably
initiated in the Late Miocene. These stratigraphic and structural
relationships indicate a Middle Tertiary, possibly Oligocene age,
for the lava flows.
73
Unconsolidated Sediments
Much of the thesis area is covered by deposits of unconsoli-
dated sediments. Quaternary alluvium, pediment gravels, and landslide deposits occur in the area.
Quaternary alluvium, in the form of unconsolidated gravel,
sand and silt, is found along some of the larger streams within the
area (Plate 3). Deposits in the smaller and steeper stream valleys
are composed of angular boulders and cobbles of sandstone, limestone or lava rock, depending on the available rock type, in a matrix
of sand- and silt-size material. These deposits are of a colluvial
nature and the sedimentary materials have undergone little or no
stream transportation.
The terrace, pediment, and landslide deposits occurring in
the mapped area have been discussed in the Geomorphology section.
74
STRUCTURAL GEOLOGY
The High Plateaus of central Utah are a structural transition
zone between the block faulted, thick geosynclinal sedimentary rocks
of western Utah and the less-deformed and thinner shelf sequences of
the Colorado Plateau.
Regional Structure
The dominant structural features of the geosynclinal area west
of the High Plateaus are block faults of Tertiary age which have been
superimposed on Late Jurassic to Late Cretaceous faults and folds.
The shelf folds to the east are broad anticlinal and monoclinal flex-
ures which are characteristic of the Colorado Plateau. These flexures were formed at some time between the middle and late part of
the Paleocene (24, p. 13).
The Pavant and Canyon Ranges (Plate 2) are large uplifted
blocks on the eastern edge of the geosynclinal area which are typical
of the Basin and Range fault blocks. Within the Canyon Range thrust
faulting of early Late Cretaceous age is exposed disclosing Precambrian rocks overlying Late Cretaceous conglomerates of the Indianola
Group. The Gunnison Plateau and the Valley Mountains, located
west of the Sevier and Sanpete Valleys, are smaller uplifted fault
blocks (Plate 2).
The most prominent structural feature east of the High Plateau is the San Rafael Swell. The Swell is an elongate northeast-
trending anticline with a steep east flank and a gently dipping west
75
flank. The Book Cliffs which circle the northern part of the San
Rafael Swell form the east side of the High Plateaus.
The outstanding structural features of the central and northern High Plateaus are the Wasatch monocline and the normal faults
which are superimposed on it. On the eastern side of the Wasatch
Plateau the strata dip gently westward from the San Rafael Swell and
on the western side the strata dip more steeply into the Wasatch
monocline. The Wasatch monocline forms the west front of the
Wasatch Plateau from north of Fairview, Utah to south of Salina
Canyon where it is masked by Tertiary volcanic rocks.
Superimposed
on the monoclinal structure are numerous normal faults with displacements as great as 3, 000 feet.
The major faulting was initiated
in the Early Tertiary and continued into the Pleistocene.
Four major periods of deformation have been recognized in
the
region. The first occurred between the Late Jurassic and early
Late Cretaceous (prior to Colorado time), and formed the Sevier
Arch. The second happened during the middle Late Cretaceous
(middle Montana time).
orogeny by Spieker
This has been named the Early Laramide
(23, p. 79). The third, between the Late
Eocene and the Miocene, produced the Wasatch monocline.
The
last, during the Late Miocene, initiated the normal faulting of the
High Plateaus. Spieker (23, p. 77-81) has outlined the sequence of
deformation in the region and presents evidence for 14 distinct
periods of crustal movement.
76
Thesis Area Structure
The northern part of the Fish Lake Plateau lies in a transition
zone between the simple domal uplift of the San Rafael Swell of the
Colorado Plateau Province on the east and the highly faulted, structurally complex region of the Great Basin Province on the west. Be-
cause of its transitional location the Fish Lake Plateau has structural
elements characteristic of both bordering areas.
The central and western parts of the mapped area are dominated by a homoclinal sequence of west-dipping Late Cretaceous and
Early Tertiary strata which are modified by Late Tertiary normal
faults. The homoclinal structure is the gently dipping limb of the
Wasatch monocline and is similar to the monoclinal folds of the
Colorado Plateau. The Gates Creek monocline, located in the west-
central part of the region (Plate 3) is a minor flexure of the same
type.
Folds
Wasatch Monocline
The Wasatch monocline is the dominant feature of the northern High Plateaus of Utah. It forms the western front of the Wasatch
Plateau between Milburn, Utah and Salina Canyon, a distance of 55
miles. South of Salina Canyon the monocline becomes less pronounced due to a lesser structural development and to an overlapping
by Tertiary volcanics. The difference in structural elevation between
the flat-lying strata at the top of the High Plateaus to where the
77
gently dipping beds of the Green River Formation pass under the
alluvium of Sevier and Sanpete Valleys (Figure 19) exceeds 6, 000
feet.
The strata are generally horizontal in the eastern part of the
area and the beds begin to dip to the west on the western side of Brown's Hole
(Plate 3). The strata are gently inclined to the west with dips that
are only locally greater than 100. In the northern part of the area
the monocline is well developed but in the southern part the monocline cannot be recognized. This is partly because of the volcanic
cover in the extreme southern part of the area, and partly because
of a lesser structural development.
Spieker (23, p. 44-48), in discussing the monocline, suggests that it is a tensional rather than a compressional feature, and
that its origin is distinctly different from that of the typical Colorado
Plateau monoclines which were caused by deep-seated compression.
Spieker believed that the Wasatch monocline and the associated
grabens of the High Plateaus were the result of regional uplift that
took place after the deposition of the Late Eocene Crazy Hollow For-
mation and before the deposition of the Tertiary lavas of probable
Oligocene age. Because the age of the volcanics is uncertain
Spieker (23, p. 80) places the time of folding between the Late Eo-
cene and the Miocene and suggests that an early date in this interval
is likely. McGookey (16), however, states that relationships observed in regions immediately west of the thesis area indicate that
the folding followed the deposition of the "Bullion Canyon volcanics,
clastics", and that this indicates a probable early Oligocene age for
78
the folding. No data within the mapped area was observed which
could establish the time of folding any closer than that suggested by
Spieker.
Gates Creek Monocline
In T. 22 and 23 S., R. 1 and 2 E. (Plate 3) is another monoclinal flexure which McGookey (16) has named the Gates Creek monocline. The monocline has been developed en echelon to the southern
end of the Wasatch monocline and was probably formed at the same
time. The dips east of the shoulder range from 4° to 100 west. At
the steepest part, farther west in the vicinity of Gates Creek, the
dips increase and range from 18° to 36° west. The toe'of the fold is
located west of the thesis area and is characterized by dips of less
than 10°. To the north the fold dies out, but to the south the bedrock
is covered by landslide debris. The origin and time of folding of the
structure are believed to be the same as those of the Wasatch monocline.
Other Folds
At the head of Porcupine and Hoodoo Creeks in T. 22 S., R.
2 E. there is a half-dome-shaped structure. From south to north
the strikes of the strata change from N 40° W to N 50° E, and the
dips range from 8° to 15° west. To the west the fold dies out in
Gooseberry Valley by merging with the regional homoclinal struc-
ture, and to the east it is bounded by a normal fault. All indications
suggest that the structure is a pre-faulting flexure and it is believed
79
to have been formed by the same forces that produced the Gate Creek
monocline.
Local reversals of dip, associated with normal faults, are
common in the area. A number of these dip reversals are associated with the Water Hollow graben. These reversals are drag folds
which are a result of differential movement along fault planes. An
excellent example of a drag fold is exposed in Salina Canyon (NE 1/4,
SE 1/4, sec. 13, T. 22 S., R. 2 E.) where beds of the Blackhawk
Formation are seen to dip steeply into a north-trending fault (Figure
20).
Faults
The Wasatch and Fish Lake Plateaus are characterized by
groups of north- and northeast-trending high angle normal faults.
These faults are considered to represent the easternmost extension
of the Basin and Range type of faulting. Five major grabens have
been developed in the Wasatch Plateau and three of these extend
southward into the Fish Lake Plateau (23, p. 42-44). Of these three
only the Water Hollow graben is entirely within the thesis area. The
western boundary fault of the Musinia graben forms the eastern
boundary of the mapped area.
The age of the faulting can only be determined by structural
and geomorphic relations. There is no evidence in the area of
faulting prior to the extrusion of the Tertiary lavas which are considered to be of Early Oligocene age. Pediments which have been
affected by the faulting also aid in the dating of the structures as
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81
they were formed after the extrusion of the lavas but prior to the
faulting. Between Yogo and Niotche Creeks in T. 23 S., R. 3 E. a
perched pediment forms Flat Top Mountain. At the base of the west
boundary fault of the Musinia graben there is a pediment which is
believed to correlate with the pediment of Flat Top Mountain. This
correlation is based on the following facts: 1) the present difference
in elevation between the pediments is about the same as the displace-
ment of the fault, 2) the pediments are both formed on strata of the
Late Cretaceous and Early Tertiary North Horn Formation, and 3)
only one period of pediment development, during the Quaternary, has
occurred in the area. The fact that Niotche and Yogo Creeks cut
diagonally across the faults indicate that the major drainages were
established prior to the faulting.
Taking all of the data into consideration it appears that the
normal faulting was initiated after the extrusion of the lavas and
sometime after the present drainage pattern was well developed,
probably in the late Miocene. Faulting has continued into the
Recent in the region, but no positive evidence of this was found in
the mapped area.
Musinia Graben
The north-trending west boundary fault of the Musinia graben
forms the east boundary of the thesis area. At the eastern end of
Salina Canyon (Plate 3) the fault has a displacement of at least 1, 000
feet (23, p. 44) and possibly as much as 2, 000 feet. The fault forms
a cliff composed of sandstones of the Price River Formation
82
(Figure 21). This cliff forms the western boundary of a broad valley
formed by the erosion of the less resistant North Horn Formation.
To the north the fault continues into the Wasatch Plateau and to the
south the displacement becomes progressively less until the fault
trace disappears under landslide debris in the southern part of T. 23
S. ,
R. 3 E.
Water Hollow Graben
The Water Hollow graben occupies a fault zone approximately
one and one-half to two miles wide in the north-central part of the
area. The zone is separated from the Musinia graben by two and
one-half miles of relatively unbroken terrain. The graben is formed
by one main fault on the east side and by three subsidiary faults to
the west. As fault surfaces are rarely visible because of erosion
and sliding the fault traces were mapped by photo interpretation. The
fault planes are generally nearly vertical or dip steeply to the east.
The westernmost fault, as seen in Salina Canyon, has a 600 dip to
the east but becomes nearly vertical to the south. The faults which
were photo interpreted apparently have dips ranging from 600 east
to vertical.
Displacement along the easternmost fault is about 1, 000 feet.
The eastern block in the graben has had the greatest displacement,
and the blocks to the west have progressively less displacement.
Brown's Hole (Plate 3) is a distinctive topographic feature formed
on the easternmost block as a result of the differential erosion of the
less resistant North Horn Formation (Figure 22). The cliffs on
a1
FIGURE 21. A view west down Salina Canyon showing the fault-line scarp of the, western boundary
fault of the Musinia graben. The cliffs in the background are formed by strata of the Blackhawk and
Price River Formations. The valley in the foreground has been formed on less-resistant strata
of the North Horn Formation.
tTä
FIGURE 22. A view to the north into Brown's
Hole, a topographic basin formed by erosion
of the North Horn Formation in the Water Hollow graben.
84
either side of Brown's Hole are composed of the sandstones of the
Price River Formation. South of Brown's Hole the graben is difficult
to recognize as the displacement decreases and there is no longer a
prominent physiographic expression.
From Salina Canyon to about two miles south, the Water Hol-
low graben is cut by a number of smaller faults. These faults have
no consistent trend and form small fault blocks with strata dipping in
a variety of directions. Only the more prominent of these faults have
been included on the geologic map because of scale limitations.
These smaller fault blocks as well as the three major fault blocks
appear to be foundered blocks formed by tensional release rather
than by differential uplift.
Many other normal faults occur in the mapped area (Plate 3)
and they are believed to be the result of the same forces which formed the major grabens. The isolated faults may be later than the major graben faulting but no evidence to this effect has been observed
in the mapped area.
85
GEOMORPHOLOGY
Stream Erosion
This region, largely mountainous, is highly dissected by
stream erosion. In the northern part the streams have cut steep
walled canyons and have narrow, flat, interstream divides, while in
the southern part the streams have cut broader valleys and have
rounded interstream areas. In the northwestern part of the area,
Gooseberry Creek has formed a relatively wide valley attaining a
maximum width of about one mile near its junction with Salina Creek.
Farther south Gooseberry Valley narrows rapidly and the gradient
of the creek increases. In general, it appears that the thesis area
is in the late youth to early maturity stage of stream erosion.
Many of the streams flow to the north and are subsequent to
the north-trending regional structure. Their courses have been de-
termined either by differential erosion of the predominantly northtrending and west-dipping strata or by north trending normal faults.
Other streams, such as the northeast-flowing Niotche Creek and the
west-flowing Salina Creek, are antecedent streams cutting across
the north-trending normal faults. The antecedent drainages appear
to have been well established as early as the Late Miocene when the
normal faulting, which strongly affected the area, began.
Terraces indicate that there were at least two periods of
stream erosion during the Late Cenozoic, prior to the deposition of
Quaternary alluvium. Arroyos now being cut into the Quaternary
alluvium, indicate that a new cycle of erosion has begun. The
86
down-cutting is probably due to a lowering of a temporary base level
or to recent uplift.
Terraces
Alluvial terraces occur along two stream valleys within the
mapped area. They are composed of boulders and cobbles of andes-
ite, latite, and sandstone in a matrix of quartzite and chert pebbles
and coarse sand. A discontinuous terrace, about 15 to 20 feet above
the present stream level, lies along Gooseberry Creek in the northwestern part of the area (Plate 3). The terrace is first noticed at
the Gooseberry Creek Ranger Station where it is about one-half mile
long, a few hundred yards wide, and is restricted to the west side
of the creek.
About a mile downstream the terrace again occurs on the
west side of the creek and widens as the creek enters the southern
end of Gooseberry Valley. In the valley the terrace is found along
both sides of the creek and attains a width of one half mile (Plate 2).
The surface of the terrace is relatively flat and slopes to the north
at the same gradient as the creek. One-half mile east of Gooseberry
Creek, at the mouth of the canyon formed by Porcupine Creek
(Plate 3), a deposit of cobbles and gravel has been interpreted by
the writer to be an erosional remnant of the Gooseberry Creek
terrace.
Another terrace, about two miles long and one half mile
wide, occurs on both sides of the northeast-flowing Yogo Creek in
the extreme east central part of the mapped area (Plate 3).
87
The terrace deposits within the area record an earlier period
of sedimentation during which the stream valleys were partially filled
with coarse-grained deposits. These deposits were nearly completely removed during a later period of erosion. This episode of valley
filling was post-normal faulting and pre-Quaternary alluvium, sug-
gesting a Pleistocene age for the terraces.
Pedimentation
Pediments, which are formed as gently sloping plains eroded
at the foot of steep slopes or cliffs, are found in the southeastern
and eastern parts of the mapped area (Plate 3) at elevations ranging
from 7, 000 to 10, 000 feet. The steep slopes or cliffs which are
associated with pediment development have been removed by erosion
and the pediments remain as the only indication of these previous
topographic highs.
The pediments are formed predominantly on the sedimentary
rocks of the Late Cretaceous North Horn Formation, but in the ex-
treme southern part of the region a pediment is formed in part on
strata of the Early Tertiary Flagstaff Formation. The pediments
are covered by 5 to 20 feet of gravel composed of rounded pebbles
of chert and quartzite and angular to sub-angular cobbles and bould-
ers of andesite and latite. The pediment surfaces are generally inclined to the northeast with slopes of four to eight degrees.
The largest pediment surface in the area forms Flat Top
Mountain, a distinctive topographic feature lying between Niotche
and Yogo Creeks in the southeastern part of the area (Figure 23).
FIGURE 23. A pediment surface between Niotche and
Yogo Creeks which forms Flat Top Mountain. The
pediment surface is formed on strata of the North Horn
Formation.
'89
This pediment trends in a northeastern direction, is nearly four
miles long and varies in width from one-eighth to three-quarters of
a mile. The southwestern end of the pediment has been displaced by
a fault associated with the Water Hollow graben. Numerous smaller
pediments occur as isolated topographic highs within the extensive
area of landsliding between Table Mountain and the steep cliffs of the
lava-covered plateau to the south (Plate 3).
Narrow pediment surfaces lie at the base of the western
boundary fault of the Musinia graben along the eastern edge of the
mapped area. The pediments are terminated upslope by the fault and
are formed on strata of the North Horn Formation. They must have
been formed at a higher elevation, later being displaced to their
present position by normal faulting.
The pediment surfaces are covered by cobbles and boulders
of volcanic material indicating that the pediments were formed after
the extrusion of the Oligocene lavas. Since faulting the pediments
have been extensively dissected by stream erosion.
Landsliding
Extensive landsliding has occurred within the thesis area,
particularly south of the Gooseberry Ranger Station where three
quarters of the land surface is covered by landslide debris. The
landslide areas are characterized by hummocky topography, interrupted drainages and by numerous closed depressions, some of
which form small ponds and lakes. Below 9, 000 feet the landslides
typically are covered by growths of aspen, while above 9, 000 feet
90
the slide areas are open, grass-covered slopes (Figure 24) with
aspen growing in profusion along the creeks.
Though landslide scars are common and a few minor slump
blocks are present, there is little evidence of recent landsliding of
the scale necessary to account for the extensive slide areas that are
present. The writer believes that at the present time landsliding is
a minor feature and that the major landsliding took place in the late
Pleistocene when the amount of precipitation in the area was much
greater.
Most of the slides involve the Late Cretaceous North Horn
Formation and the Early Tertiary Flagstaff Formation. In one area
(sec. 27, T. 23 S., R. 2 E.) the Colton and Green River (?) Formations have also been affected by sliding, and it is possible that later
Tertiary formations are also involved in the landsliding though they
cannot be identified in the rubble of the landslide debris.
A major factor that influenced the sliding was the Tertiary
lava flows which covered the southern part of the thesis area and
capped the weaker underlying sedimentary rocks. Differential weath-
ering and erosion of these weaker rocks caused oversteepening of the
slopes and sapping of the lava cliffs which resulted in rock falls and
slumping.
Talus creep, caused by frost heaving, is a common feature
at the base of the lava cliffs in the southern part of the area. Rock
glaciers, composed of sinuous streams of angular blocks of lava,
extend over three-quarters of a mile from the base of the lava cliffs.
.1
FIGURE 24. A view to the north from the head
of Niotche Creek. The topography in the central
part of the photograph has been formed by landsliding. Tertiary lavas form the cliff in the left
background.
92
HISTORICAL GEOLOGY
During the Late Mesozoic a northeast-trending positive area
known as the Sevier Arch was formed in western Utah. The arch is
believed to be the third in a series of major upwarps which were
developed by the eastward progression of Paleozoic and Mesozoic
orogenies. The structural history of the Sevier Arch is described
in detail by Harris (9). After the initial uplift of the arch the orogen-
ic deposits of the Late Jurassic Morrison Formation and the Late
Cretaceous Indianola Group were deposited in a geosynclinal fore-
deep east of the arch. The deposits of the Indianola Group become
progressively finer eastward and are believed to grade into the
shales which were being deposited in the shallow Mancos Sea of cen-
tral and eastern Utah. As the highland source areas to the west were
worn down finer grained sediments were deposited in the Fish Lake
Plateau area. These deposits of fluviatile, swamp, lagoonal and
marine origin formed the Blackhawk Formation of middle Montana
age. Outcrops of this formation are not found west of the thesis area
but it is probable that they extended much farther to the west and
were subsequently removed during the Laramide folding and erosion
that took place between middle and late Montana time.
The Laramide orogeny was initiated by thrust faulting in the
area of the Sevier Arch and by folding in the area of the Sevier and
Sanpete Valleys. The folding is well exposed at the mouth of Salina
Canyon and at other localities along the west front of the Wasatch
Plateau. Within the Fish Lake Plateau area this episode of folding
93
and subsequent erosion is represented by the disconformity between
the middle Montana Blackhawk Formation and the late Montana Price
River Formation. To the west and northwest the Price River Forma-
tion is highly conglomeratic but in the Fish Lake Plateau area the
formation is predominantly sandstone which becomes finer to the
east. The Castlegate Member of the formation was deposited as a
great sandstone tongue which extends eastward across Utah into
Western Colorado where it disappears by intertonguing with the
Mancos Shale. The finer grained sediments of the Late Cretaceous
and Early Tertiary North Horn Formation were deposited conform-
ably over the Price River Formation as the highland source areas
to the west were worn down. The lower varicolored beds of the North
Horn Formation were deposited in fluviatile environments and the
upper beds were deposited under lacustrine conditions which were
initiated in this area in the Early Paleocene and prevailed until Middle Eocene time.
The post-North Horn, pre-Flagstaff regional compression
which formed the monoclines of the Colorado Plateau and deformed
areas to the north along the west front of the Wasatch Plateau did not
affect the Fish Lake Plateau area, or at least this effect does not ap-
pear in the stratigraphic record.
During the Late Paleocene and Early Eocene red silts and
clays with some calcareous beds were deposited under lacustrine
conditions in the northern part of the area and graded southward into
the typical grayish green argillaceous beds and white limestones of
the Flagstaff Formation. Following the deposition of the Flagstaff
94
Formation the lacustrine varicolored siltstones and mudstones of the
Colton Formation were deposited and were subsequently followed
without break by the green shales and white limestones of the Green
River Formation.
The deposition of the Green River Formation was followed by
a period of erosion which probably lasted until the early Late Eocene.
Following this erosion, which removed a considerable amount of the
Green River Formation, the conditions changed from lacustrine to
fluviatile and the varicolored muds and sandstones of the Crazy Hollow Formation were deposited unconformably over the eroded surface
of the Green River Formation. Renewed downwarping in the area
caused the formation of a second great lake in which the Gray Gulch
Formation was deposited. At the same time volcanic activity was
initiated in adjacent areas, supplying volcanic ash to the lake basin.
The amount of ash was sufficient to form the tuffaceous siltstones
and sandstones found within the Gray Gulch Formation.
Lacustrine conditions were terminated in the area in latest
Eocene time when large volcanoes appeared in areas to the south
and southwest. Streams from the volcanic areas carried huge quan-
tities of volcanic material into the region immediately west and possibly into the mapped area proper. The volcanic debris was deposited as mudflows which compose the "Bullion Canyon volcanics,
clastics" of McGookey (16).
A period of uplift followed the deposition of the "Bullion
Canyon volcanics, clastics", and associated forces caused the formation of the Wasatch monocline and the much smaller Gates Creek
95
monocline located on the western edge of the mapped area. The uplift and folding were followed by a period of erosion which removed
a considerable amount of strata from the central and eastern
parts of the area. After the period of erosion a thick series of lava
flows from sources in the Fish Lake and Sevier Plateaus covered the
southern and possibly the central part of the mapped area. The
flows were part of a great volcanic sequence which presently covers
over 3, 000 square miles of the High Plateaus.
A period of erosion and pediment formation followed the ex-
trusive activity. During the Late Miocene the whole region was uplifted and normal faulting began. The faulting continued into the
Pleistocene and possibly into the Recent. Extensive landsliding and
at least two cycles of stream erosion have modified the topography
during the Late Cenozoic. At the present time erosion is the dominant process as arroyos are now being cut into Quaternary alluvium.
96
ECONOMIC GEOLOGY
Limited exploration has been conducted in the northern part
of the Fish Lake Plateau in the search for oil and gas. This explor-
ation has been concentrated in the north-central part of the area along
Salina Canyon. In the past coal has been produced from mines within
Salina Canyon.
Oil and Gas
Stratigraphic and possibly structural conditions in the area
are apparently favorable for the formation and accumulation of
petroleum and gas. Both source and reservoir rocks are present
in the subsurface. However, two dry oil and gas test holes have
been drilled in the area. The locations and descriptions of these dry
holes are given in Table 3.
F. M. Christianson (4) includes the Fish Lake Plateau in a
report concerning the oil and gas possibilities of central Utah.
Possible Reservoir Rocks
About 7, 000 feet of Cretaceous sedimentary rocks are known
to underlie the area studied. Earlier Mesozoic strata outcrop both
east and west of the mapped area and an undetermined thickness of
these rocks is believed to be present in the subsurface. An additional 6, 000 feet of Late Cretaceous and Early Tertiary nonmarine rocks
are exposed in the area.
Several of the Cretaceous formations contain possible reservoir rocks. From electric log data it appears that permeable
TABLE 3. Summary of oil and gas test holes in the thesis area.
Name
Total
Location
Date
Depth
Pan American Petroleum
C, NW, NW,
1963
6299
Corp o rati on Po rcupine
Sec. 30
Ridge Unit #1
T. 22 S. , R. 3 E.
E1 Paso .Natural Gas
Com p a ny U n it #1
SW, NE, NE,
Sec. 15
T. 22 S. , R. 2 E.
1953
6116
Spudded
in
Bottomed
in
.
Price River (?)
Formation
Tununk
Shale
Blackhawk
Morrison
Forma-
Formation
tion
98
sandstone beds occur in the Late Cretaceous Sanpete, Ferron and
Star Point formations. The Late Cretaceous and Early Tertiary
Price River and North Horn formations also contain many permeable
sandstone beds but they are exposed within the mapped area. It is
very probable that other reservoir rocks are present in units of the
Indianola Group in areas to the west which have not been drilled and
at deeper horizons in strata of earlier Mesozoic age. The Mancos
Shale of Late Cretaceous age is a known source rock for petroleum
and gas in areas farther east.
Structural and Stratigraphic Traps
This area does not seem suitable for the structural entrapment of oil. The region is dominated by a homoclinal sequence of
west-dipping Late Cretaceous and Early Tertiary strata which are
modified by normal faulting. The major homoclinal structure and
some local flexures appear to be the result of regional uplift and de-
formation during the Early Oligocene. Normal faulting, initiated
during the Late Miocene, was superimposed on the earlier structures and locally caused displacements of over 1, 000 feet. The
faulting in the central part of the area has formed a closure on a
half-dome-shaped structure located at the head of Porcupine and
Hoodoo Creeks (Plate 3), and has formed many local reversals of
dip due to drag along the fault planes. Though there have been
structures with closure formed by the faulting the writer believes
that these possible structural traps have been formed too late in the
geologic history of the region to act as traps for the accumulation
99
of oil and gas.
Stratigraphic traps in the form of updip pinchouts may be
present in the area. If present they would be best developed in the
western part of the area where the writer believes that there is extensive intertonguing between the Late Cretaceous Indianola Group
and the Mancos Shale. This idea is based on the fact that strati-
graphic relations and paleontologic evidence (12) indicate that the
Indianola Group, which outcrops on the west front of the Wasatch
Plateau and is last seen in Salina Canyon, is correlative in age to
the Mancos Shale. Three miles west of the mapped area the Indian-
ola Group lies with angular unconformity beneath Early Tertiary
strata. Spieker (23, p. 66) indicates that eastward from the unconformity 5, 000 to 7, 000 feet of Late Cretaceous beds, including the
Indianola Group, flatten out and the unconformity passes into a disconformity that can be observed in the mapped region between the
early Montana Blackhawk Formation and the late Montana Price
River Formation. The El Paso Natural Gas Company test hole located in Salina Canyon recorded 365 feet of the Sanpete Formation
of the Indianola Group and the Pan American test hole three miles
southeast of the El Paso Natural Gas well recorded no strata of this
unit. Likewise the two test holes indicated a thickening of the Blue
Gate Shale Member of the Mancos Shale eastward. It appears that
within a distance of ten miles the continental facies of the Indianola
Group passes transitionally into the marine facies of the Mancos
Shale. It is probable that many littoral marine sandstone tongues
are present in the subsurface and that these units have formed
100
stratigraphic traps capable of accumulating oil and gas.
Oil and Gas Possibilities
Though two test holes have been drilled in the mapped area
with no success, the northern part of the Fish Lake Plateau is still
virgin territory for oil and gas exploration. The possible occurrence
of oil and gas in the area is strengthened by the fact that gas is produced in nearby areas. Gas is produced from the Ferron Sandstone
in the Clear Creek and Flat Canyon fields located in the northern
part of the Wasatch Plateau. In the Clear Creek field gas is also
produced from the Early Cretaceous Dakota Sandstone (29). Gas has
been discovered in the Early Triassic Moenkopi Formation on the
Last Chance Anticline located approximately eight miles southeast
of the thesis area (8).
As production has already been established for the Moenkopi,
Dakota and Ferron Formations in nearby areas there seems to be
little reason to doubt the potential of these units in this area. Further study and drilling within the Fish Lake Plateau may very possibly locate stratigraphic traps in the form of updip sand pinchouts.
Coal
Many thin coal beds occur in the area within. the Blackhawk
Formation. These deposits, which are best exposed in Salina Can-
yon, have been investigated and described by Spieker and Baker
(25).
During the 1920's some small prospects and coal mines were
operated in Salina Canyon and one, the Sevier Valley Coal Company
101
mine, located in sec. 12, T. 22 S., R. 3 E. remained in operation
until 1940. Currently there are no mines operating in the area but a
few miles to the east coal is being mined from both the Blackhawk
and Ferron Formations. The Pan American Petroleum test hole penetrated a few thin coal beds in the Ferron Sandstone.
Since most of the coal beds in the area studied are thin and
local in nature it is doubtful that coal mining will ever become an
important industry.
103
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